Puffy skin disease (PSD) in rainbow trout, Oncorhynchus mykiss (Walbaum): a case definition

Puffy skin disease (PSD) is a disease that causes skin pathology in rainbow trout, Oncorhynchus mykiss (Walbaum). Incidence of PSD in UK fish farms and fisheries has increased sharply in the last decade, with growing concern from both industry sectors. This paper provides the first comprehensive case definition of PSD, combining clinical and pathological observations of diseased rainbow trout from both fish farms and fisheries. The defining features of PSD, as summarized in the case definition, were focal lateral flank skin lesions that appeared as cutaneous swelling with pigment loss and petechiae. These were associated with lethargy, poor body condition, inappetance and low level mortality. Epidermal hyperplasia and spongiosis, oedema of the dermis stratum spongiosum and a mild diffuse inflammatory cellularity were typical in histopathology of skin. A specific pathogen or aetiology was not identified. Prevalence and severity of skin lesions was greatest during late summer and autumn, with the highest prevalence being 95%. Atypical lesions seen in winter and spring were suggestive of clinical resolution. PSD holds important implications for both trout aquaculture and still water trout fisheries. This case definition will aid future diagnosis, help avoid confusion with other skin conditions and promote prompt and consistent reporting.

Gill pathology in Scottish farmed Atlantic salmon, Salmo salar L., associated with the microsporidian Desmozoon lepeophtherii Freeman et Sommerville, 2009

Gill disorders have emerged in recent years as a significant problem in the production of marine-stage Atlantic salmon Salmo salar L. The multi-aetiological condition 'proliferative gill inflammation' (PGI) has been reported to cause heavy losses in western Norway, yet reports of Scottish cases of the disease have remained anecdotal. In the present study, histopathological material from a marine production site in the Scottish Highlands experiencing mortalities due to a seasonal gill disease with proliferative-type pathology was examined using light microscopy, special staining techniques and transmission electron microscopy (TEM). The microsporidian Desmozoon lepeophtherii Freeman et Sommerville, 2009 (syn. Paranucleospora theridion) was identified by staining using a Gram Twort method and TEM associated with distinctive proliferative and necrotic pathology confined to the interlamellar Malpighian cell areas of the primary filaments. Epitheliocystis was not a feature of the gill pathology observed. It is believed this is the first report of D. lepeophtherii being identified associated with pathology in a Scottish gill disease case, and supports anecdotal reports that a disease at least partly synonymous with PGI as described by Norwegian researchers is present in Scottish aquaculture.

Systemic nocardiosis in a Mediterranean population of cultured meagre, Argyrosomus regius Asso (Perciformes: Sciaenidae)

Marine cultured meagre, Argyrosomus regius Asso, in central and western Greece were affected by an outbreak of systemic granulomatous disease subsequently demonstrated to be nocardiosis. The fish were originally imported as juveniles from hatcheries in France and Italy and on-grown in Greece, the latter also providing broodstock for a small number of local Greek hatcheries for the production of second-generation juveniles. The disease in cage reared fish had been present throughout the year, particularly in the 1+ and 2+ year old fish with a low to variable morbidity and 1-4% total mortality. Multiple lesions were visible externally on the skin of affected fish, with severe ulcerations and necrosis. Internally, multifocal yellowish-white nodules, 0.1-0.5 cm in diameter, were visible on the surface of several internal organs. Histopathology revealed systemic granulomatous inflammation. Fite-Faraco staining clearly demonstrated the presence of Nocardia-like organisms which were Gram-positive, long, rod to beaded filamentous bacteria. Nocardia genus-specific 16s RNA primers NG1 and NG2 were used to generate a 600 bp fragment recovered from affected tissue, confirming the diagnosis of Nocardia spp. To our knowledge, this is the first report of nocardiosis in meagre.

Ultrastructural morphogenesis of salmonid alphavirus 1

Studies on the ultrastructural morphogenesis of viruses give an insight into how the host cell mechanisms are utilized for new virion synthesis. A time course examining salmonid alphavirus 1 (SAV 1) assembly was performed by culturing the virus on Chinook salmon embryo cells (CHSE-214). Different stages of viral replication were observed under electron microscopy. Virus-like particles were observed inside membrane-bound vesicles as early as 1 h following contact of the virus with the cells. Membrane-dependent replication complexes were observed in the cytoplasm of the cells, with spherules found at the periphery of late endosome-like vacuoles. The use of intracellular membranes for RNA replication is similar to other positive-sense single-stranded RNA (+ssRNA) viruses. The number of Golgi apparatus and associated vacuoles characterized by 'fuzzy'-coated membranes was greater in virus-infected cells. The mature enveloped virions started to bud out from the cells at approximately 24 h post-infection. These observations suggest that the pathway used by SAV 1 for the generation of new virus particles in vitro is comparable to viral replication observed with mammalian alphaviruses but with some interesting differences.

Detection and identification of aquatic mycobacteria in formalin-fixed, paraffin-embedded fish tissues

The isolation of mycobacteria from field samples is problematic, and isolation of the bacterium is sometimes not even attempted. The detection of mycobacteria through traditional histology using formalin-fixed, paraffin-embedded (FFPE) tissues is neither sensitive nor specific. However, detection of mycobacterial DNA from FFPE specimens, suspected of being infected with mammalian mycobacteriosis, is a routine clinical procedure. In the present study, a polymerase chain reaction (PCR)-based method was used to detect and identify mycobacteria in FFPE specimens sampled from fish suspected of being infected with fish mycobacteriosis. A total of 45 fish tissue samples, comprising of 12 tissue samples obtained from experimentally infected fish and the remainder from fish naturally infected with mycobacteria, were analysed using a PCR protocol which amplifies a fragment of the mycobacterial 65 kDa heat-shock protein (hsp65) gene. PCR-restriction enzyme analysis and/or sequencing were employed to further analyse the PCR amplicons. The PCR results were compared with those obtained by histology and culture. Mycobacterial DNA was detected in 34 of the 45 samples examined, of which 16 samples (47%) showed granulomatous reactions on histological examination. Using histology as the gold standard, no false-negative PCR results were obtained. Also, considering the presence or absence of granulomas as a diagnostic criterion, the sensitivity and specificity of PCR in 42 of the FFPE tissues were 16/16 (100%) and 8/26 (approximately 30.8%), respectively. Corresponding microbiological cultures were available for 15 cases, of which 13 were pure Mycobacterium cultures. Of these, 13 were PCR positive (100% sensitivity and 50% specificity). The PCR-based methods used here proved sensitive, specific and rapid for the detection of mycobacteria in routinely processed paraffin wax-embedded and formalin-fixed histological samples, and the results of the study suggest that this method has potential use in retrospective epidemiological studies.

Evaluation of the INNO-LiPA mycobacteria v2 assay for identification of aquatic mycobacteria

Fifty-seven isolates of mycobacteria comprising 10 reference strains, 47 field isolates and one non-Mycobacterium isolate were screened using commercial INNO-LiPA v2 assay kits. All mycobacteria isolates tested hybridized with the Mycobacterium genus probe on the LiPA strip. All M. marinum, M. fortuitum and M. chelonae reference and field strains and three out of the four M. gordonae isolates hybridized to their corresponding species- or complex-specific probes. Two cultures (a type strain and a field isolate) yielded mixed growth of two mycobacterial species, i.e. M. chelonae and M. fortuitum. A Mycobacterium isolate from one of these cultures was subsequently purified and correctly identified with the kit. However, sequence analysis of the 16S-23S rRNA internal transcribed spacer (ITS) region of various mycobacteria isolates revealed a misidentification of M. shottsii and M. pseudoshottsii with the kit because these isolates reacted with the M. marinum/M. ulcerans probe. Moreover, nine of the 13 field isolates presumed to be M. fortuitum from the results of the kit had closer ITS sequence homology with M. conceptionense, a species which, to our knowledge, has never been reported in fish. These findings highlight the need to redesign the M. fortuitum-M. peregrinum probe included in the INNO-LiPA assay and to introduce additional complex-specific probes into the kit. Nevertheless, the kit proved to be a rapid and reliable method for identifying mycobacteria in the aquatic environment and would be particularly useful in laboratories without sequencing facilities.

Identification of B-cell epitopes on the betanodavirus capsid protein

The pepscan procedure was used to identify betanodavirus B-cell epitopes recognized by neutralizing mouse monoclonal antibodies (MAbs) and serum samples obtained from sea bass, Dicentrarchus labrax, naturally infected with betanodavirus. Pepscan was performed with a panel of thirty-four 12-mer synthetic peptides that mimicked the entire betanodavirus capsid protein. Sea bass serum samples reacted strongly with three regions of the capsid protein comprising amino acid residues 1-32, 91-162 and 181-212. The latter region was also recognized by neutralizing MAbs and coincided with a region of high antigenic propensity identified by an antigen prediction algorithm. These data suggest that a region of the betanodavirus capsid protein spanning amino acid residues 181-212 may represent a neutralization domain that could potentially be used to inform the development of nodavirus vaccines and immunodiagnostic reagents.

Spontaneous resolution of solitary osteochondroma in the young adult

Spontaneous resolution of a solitary osteochondroma is rare. Such a case is presented in a patient nearing skeletal maturity. Based on a search of the English literature this is the first such report in a patient of this age.

Radiological outcome of innocent infant hip clicks

Radiographic follow-up is questioned for infants with hip clicks who have normal results from ultrasound scan examination of the hips. Infants whose sole risk factor for developmental dysplasia of the hip was a soft tissue hip click who had a normal ultrasound scan on initial assessment were identified. A follow-up 6-month pelvis radiograph was assessed. The acetabular index, position of femoral ossific nucleus and Shenton's line were measured. Rotated radiographs were excluded. One hundred and seventy-one infants (193 clicking hips) met the criteria for inclusion. All parameters measured were within normal ranges. In this study infants with hip clicks and a normal hip ultrasound scan on initial assessment had a normal radiograph at 6 months.

Characteristics of a new reovirus isolated from epizootic ulcerative syndrome infected snakehead fish

Epizootic ulcerative syndrome (EUS) has been infecting a wide range of fishes in the South and Southeast Asia for the last 2 decades. One reovirus-like agent (snakehead reovirus, SKRV), isolated from an EUS-infected snakehead fish and investigated in the present study, is the only reovirus so far isolated from an EUS-infected fish. SKRV was characterised by the presence of a double-stranded RNA genome with icosahedral symmetry and double capsid. The virus had an average size of 71 nm, a buoyant density of 1.36 g ml(-1) in CsCl and lacked a lipid-containing envelope. Apart from the above, the presence of a segmented genome and structural proteins falling into 3 specific size classes confirmed that the virus belongs to the family Reoviridae. SKRV differed from aquareoviruses by the lack of a cytopathic effect (CPE) with syncitium formation and in the segmentation pattern of RNA genome. The resistance to pH (3.0 to 9.0) and heat treatment and inability to multiply in mammalian cell lines and haemagglutinate human 'O' red blood cells (RBCs) differentiated SKRV from the rest of the similar genera in the family Reoviridae. Serological comparison indicated the antigenic distinctness of the isolate from selected American and European aquareoviruses. SKRV grew well in SSN-1 and SSN-3 cells at 25 to 30 degrees C but not in the most common Aquareovirus susceptible coldwater fish cell line--CHSE-214.

Phylogenetic and antigenic characterization of new fish nodavirus isolates from Europe and Asia

Nodaviruses are widespread causative agents of viral nervous necrosis in fish. Based on the coat protein sequence, fish nodaviruses are categorized into four different genotypes. In this study, we present data on the phylogenetic and antigenic characterization of 12 new isolates, eight European and four of Asian origin, from farmed and wild species of fish. Phylogenetic analysis based on the nucleotide sequence (688 bases) of the coat protein classified the majority of these new isolates to the RGNNV genotype. Geographic or host-species specificities were not revealed by this study. Neutralizing assay experiments, further confirmed the genotypic classification, supporting the possibility that the different nodavirus genotypes can also be serologically distinguishable.

In situ hybridisation identifies the gill as a portal of entry for PKX (Phylum Myxozoa), the causative agent of proliferative kidney disease in salmonids

PKX (Phylum Myxozoa) is an important pathogen affecting salmonid culture in Western Europe and North America. All of the available oligonucleotide probes developed for the PCR amplification of PKX DNA were examined for their ability to detect PKX in fixed tissue sections using in situ hybridisation. Out of the 12 probes examined, only four stained PKX in tissue sections. The specificity of these probes to PKX was examined by testing them individually against a range of myxosporean infections. One of the probes (1032) cross-reacted with Sphaerospora truttae infecting brown trout kidney and stained this parasite in tissue sections, while probe 6R stained stickleback DNA. The results from these studies allowed for an optimised, relatively rapid, in situ hybridisation protocol to be developed for PKX detection. Using this protocol, a preliminary study was conducted on the life history of the parasite in the rainbow trout Oncorhynchus mykiss. This demonstrated the presence of PKX in the gill arch 3 days after initial exposure in an enzootic river. It is suggested that a portal of entry for PKX is the gill. From here. it migrates to the kidney where the disease progresses as previously described.

Commercial trials using emamectin benzoate to control sea lice Lepeophtheirus salmonis infestations in Atlantic salmon Salmo salar

Two trials were conducted at commercial salmon farms to evaluate the efficacy of emamectin benzoate (Slice, 0.2% aquaculture pre-mix, Schering-Plough Animal Health) as a treatment for sea lice Lepeophtheirus salmonis (Krøyer) and Caligus elongatus Nordmann infestations in Atlantic salmon Salmo salar L. Trials were carried out in 15 m2 commercial sea pens, at temperatures of 5.5 to 7.5 degrees C and 10.8 to 13.8 degrees C. Each pen was stocked with 14,000 to 17,500 fish with mean weights of 0.44 to 0.74 and 1.33 to 1.83 kg. Fish were naturally infested with sea lice at the start of each trial. At Day -1, samples of 10 or 15 fish were taken from each pen to determine pre-treatment numbers of lice. Emamectin benzoate was administered in feed, to 4 replicate pens, at a dose of 50 micrograms kg-1 biomass d-1 for 7 consecutive days (Days 0 to 6). Sea lice were counted again, between Days 7 and 77, and comparisons made with untreated control fish. Despite adverse weather conditions, wide variations in fish weights and exposure to new infestations, treatment was effective against chalimus and motile stages of L. salmonis. In the autumn trial, efficacy at Day 27 was 89%, and lice numbers remained lower on treated fish than on control fish 64 d from the start of treatment. In the winter trial, reductions in lice numbers at low temperatures were slower but good efficacy was achieved by Day 35. Although control fish had to be treated with hydrogen peroxide at Day 21, fish treated only with emamectin benzoate on Days 0 to 6 still had 89% fewer lice than control fish at Day 35. There were very few C. elongatus present, but at the end of both trials numbers were lower on treated fish. No adverse effects were associated with treatment of fish with emamectin benzoate.

Observations on the electron-dense bodies of the PKX parasite, agent of proliferative kidney disease in salmonids

Ultrastructural observations on structures associated with the 'haplosporosome'-like electron-dense bodies (EDBs) of the primary cell of the extrasporogonic stage of PKX are described. Observations made include formation of EDBs by the trans-Golgi network, an additional membrane associated with EDB structure, confronting cisternae, engulfment and presence of EDBs in multivesicular bodies, fusion of EDBs with the plasmalemma, degeneration of EDBs in disintegrating primary cells and endocytosis of PKX cytoplasm by adherent macrophages. Immunogold localisation of a PKX-specific monoclonal antibody (MAb A3) suggests that the EDBs contain periodate-sensitive carbohydrates on their membranes. Tissues prepared for immunogold electron microscopy further suggest that some contain a lipid-rich core. An interpretation is made on their possible function and their relationship with the haplosporosomes and sporoplasmasomes found in members of the Haplosporidea and Myxosporea respectively.

Induction of nodavirus disease in seabass, Dicentrarchus labrax, using different infection models

The aim of this study was to investigate the susceptibility of juvenile and adult seabass, which are generally thought to be refractory to nodavirus. Moreover, preliminary immunological studies were performed to examine the immune response of adult seabass. Successful transmission of the disease was experimentally demonstrated in juvenile and adult seabass as ascertained by the presence of the clinical signs of the disease, re-isolation of the virus in the SSN-1 cell line and subsequent confirmation by histopathology and immunohistochemistry. Bigger seabass not only developed the clinical disease but also suffered mortalities. Serum neutralisation titres were considered low in this study.

Characteristics of a new birnavirus associated with a warm-water fish cell line

A warm-water fish cell line developed from blotched snakehead caudal peduncle (BSN) was found to have persistent birnavirus infection. Purified virus particles were of icosahedral shape and had 57+/-1.6 nm diameter. The BSN virus was resistant to 5-iodo-2'-deoxyuridine and induced yellowish-green cytoplasmic inclusions when stained with acridine orange. The virus was resistant to chloroform, acid and alkaline pH and heat treatment at 56 degrees C for 2 h. Purified virions had a buoyant density of 1.33 g/ml in CsCl and contained two genomic segments with molecular masses of 2.56 x 10(6) and 2.00 x 10(6) Da and four structural polypeptides of 112 (polyprotein, PP), 91 (VP1), 44 (VP2) and 37 (VP3) kDa. Reciprocal beta cross-neutralization tests incorporating four classical strains of infectious pancreatic necrosis virus (IPNV) (WB, Sp, Ab and TV-1) and the BSN virus established the complete serological distinctness of the virus from IPNV. Considering the uniqueness of the virus, the name blotched snakehead virus is proposed for this agent.

Histopathological and electron microscopical observations on rainbow trout fry syndrome

Rainbow trout (Oncorhynchus mykiss) fry and fingerlings with clinical signs of rainbow trout fry syndrome, and rainbow trout (0.5 to 3.5 g) with experimentally induced infections with Flavobacterium psychrophilum, were examined histopathologically and electron microscopically. Severe hypertrophy of the spleen and cellular degeneration were consistently observed. Distinctive features of the disease were the loss of definition of the splenic border and its replacement by a loosely structured eosinophilic layer, fibrinous inflammation and intercellular oedema within the spleen, and the presence of numerous filamentous bacteria interspersed throughout the organ.

Haemorrhagic smolt syndrome: a severe anaemic condition in farmed salmon in Scotland

Farmed pre-smolt stage Atlantic salmon developed an acute, severe haemorrhagic anaemia, termed haemorrhagic smolt syndrome. The fish were in good condition, but lethargic, and had widespread visceral and muscle petechiation and ecchymoses. The mean (sd) haematocrit of affected fish was 1.4(0.9) per cent and histopathology revealed widespread haemorrhage in all organs, associated with endothelial tissue. No infectious agent was isolated and the condition could not be transmitted experimentally. The clinical evidence indicates that the condition is non-infectious, but its aetiology could not be fully established.

Electron microscope studies of the in vitro phagocytosis of Mycobacterium spp. by rainbow trout Oncorhynchus mykiss head kidney macrophages

The cytological response of rainbow trout Oncorhynchus mykiss head kidney macrophages to ingested Mycobacterium spp. was examined in vitro. Mycobacterium marinum or Mycobacterium sp. TB267 isolated from snakehead fish Channa striata Bloch were opsonised with either fresh rainbow trout serum, serum which had been heat-inactivated, or rainbow trout antiserum against the extracellular products (ECP) of the 2 Mycobacterium spp. A monoclonal antibody against the ECP was also used as an opsonin. Suspensions of macrophages were prepared (1 ml of 1 x 10(7) cells ml-1), mixed with the opsonised bacteria (100 microliters of 2 x 10(9) ml-1), and incubated at 18 degrees C for 0.5, 1, 2, 4 or 6 h to allow phagocytosis to occur. A quantitative evaluation of the phagocytosis of the mycobacteria by the macrophages was carried out by electron microscopy. Macrophage phagosomes and their contents were examined and numbers of intact and partially degraded bacteria determined. Pre-labelling dense granules (secondary lysosomes) with ferritin enabled phagosome lysosome fusion to be identified and their frequency determined. Opsonisation of the mycobacteria was found to greatly enhance the phagocytic and killing activity of the rainbow trout macrophages.

Amoxicillin concentrations in the serum of Atlantic salmon (Salmo salar L) during furunculosis therapy

The effectiveness of the delivery of amoxicillin to Atlantic salmon, undergoing chemotherapy in natural outbreaks of furunculosis in sea-cages, was investigated by measuring the concentration of the drug in serum samples. Five groups of 50 sera from three outbreaks were collected two hours after oral treatment with doses of 80 or 120 mg/kg bodyweight. Amoxicillin was detected in 82, 82, 92, 100 and 90 per cent of the sera in the five groups (limit of detection 0.16 microgram/ml). Many sera contained less than the minimum inhibitory concentration of amoxicillin for the causative agent Aeromonas salmonicida (0.3 microgram/ml), but a concentration more than double the minimum inhibitory concentration was achieved in 2, 2, 56, 32 and 44 per cent of the samples. There was wide variation in the serum concentrations between individuals in the same population and between populations receiving the same treatment; this variation was associated with population factors, the severity of infection and the accuracy of medicating the feed.

Occurrence of cataracts in triploid Atlantic salmon (Salmo salar) on four farms in Scotland

In September 1991 cataracts occurred in two year-classes of triploid Atlantic salmon. The fish showed varying degrees of blindness, were lethargic and became emaciated owing to their inability to feed. The lesions in the lens were mainly in the anterior and posterior cortex and perinuclear areas, the capsule and embryonic nucleus remaining unaffected. Diploid fish of the same year-class did not have cataracts. The origin of the triploid fish, the method of triploidisation, their diet and disease status were investigated, but no predisposing factors could be found to account for the high incidence of cataracts.

Amoxycillin in the control of furunculosis in Atlantic salmon parr

The efficacy of amoxycillin in the control of laboratory induced Aeromonas salmonicida infection in Atlantic salmon parr was investigated. When given in the diet at a dose rate of 80 mg per kg bodyweight it was effective against both a moderate and severe challenge (with mortality rates in untreated groups of 75 per cent and 45 per cent). At 40 mg per kg it was effective against the moderate challenge only. The plasma levels in these regimens were 1.25 micrograms per ml and 0.3 to 0.6 micrograms per ml and the minimum inhibitory concentration of the challenge strain of A salmonicida was 0.6 micrograms per ml. The potential of the Charm radiobioassay system in detecting antibiotic residues in fish tissue was studied. The level of amoxycillin in muscle and bone from fish in mid-treatment at 80 mg per kg was 0.32 micrograms per ml. After a 12 day withdrawal period at 18 degrees C no residue was detected within the 0.005 micrograms per ml limit of this test.

Observations on removal of metal implants

A total of 86 adult patients who underwent routine surgery to remove metal internal fixation devices were studied prospectively. At the time of surgery, 46 patients were symptomatic, but only 27 requested surgery; 59 were admitted for routine surgery on medical advice. There was no correlation between symptoms, the length of time the implant had been in situ or the location of the implant. Good results were achieved in 91 per cent of symptomatic patients and no problems occurred in 95 per cent of asymptomatic cases. Overall there was a 3 per cent complication rate including one refracture, one radial nerve injury and one haematoma. No wound infections occurred. Potential difficulties in the removal of implants and possible risks of retained implants are discussed, relating to refracture, osteopenia, metal toxicity and neoplasia. In conclusion, it may be appropriate to leave asymptomatic implants in situ, except for femoral and tibial diaphyseal plates.

Septic arthritis caused by Corynebacterium xerosis following vascular surgery

A case of septic arthritis due to Corynebacterium xerosis occurred after vascular surgery and was successfully treated with intravenous cefotaxime followed by oral erythromycin. The only previously reported case of C. xerosis arthritis developed in a patient with a history of similar recent surgery. The possible association of this infection with such a postsurgical setting is discussed.

Proliferative fasciitis of a finger: a case report

This is the first report of proliferative fasciitis presenting in a finger. This is a benign pseudosarcomatous lesion which normally runs a self-limiting course.

The AO dynamic hip screw and the Pugh sliding nail in femoral head fixation

We compared, under laboratory conditions, the resistance to cutting out of the AO dynamic hip screw and the Pugh sliding nail. The mean load at cut out, adjusted for bone strength, was 70% greater for the Pugh sliding nail. The reasons for this difference are discussed.

Acetate levels in human plasma

We have developed a gas liquid chromatographic assay for plasma acetate which detects 0.01 mM and has a standard deviation of less than 16% of the mean at 0.05 mM. The acetate concentration of venous blood obtained from normal subjects was 0.025 +/- 0.002 mM. The value was not significantly different from the venous acetate concentration of dialysis patients, prior to a dialysis treatment. The acetate concentration of arterial plasma obtained from dialysis patients prior to a hemodialysis treatment was 0.048 +/- 0.006 mM. This was significantly greater than the venous concentration of 0.027 +/- 0.002 (p less than 0.01). This arteriovenous difference suggests that acetate is utilized peripherally. At the onset of hemodialysis, acetate concentrations rapidly rose and, in all but one case, reached a steady state value in the range of 1.5-5.1 mM. At the termination of dialysis, acetate concentrations fell rapidly, usually achieving baseline values within one hr. The rate of decrease was not a simple logarithmic function, suggesting that acetate metabolism is not solely a first order function. Furthermore, acetate disappearance was more rapid in the dialysis patients than in the normal subjects. We wish to emphasize that the present data, which were obtained on a small number of subjects are preliminary and should be interpreted with caution.