1. Selenium status was investigated in patients with chronic renal failure, with special regard to its relations to the dialysis treatments, dietary habits and clinical signs of atherosclerosis. 2. Serum selenium concentration and platelet glutathione peroxidase activity were measured in 45 patients with chronic renal failure subdivided into three groups according to the type of treatment: 15 non-dialysed, 15 on haemodialysis, 15 on continuous ambulatory peritoneal dialysis. A 7-day diet history was carried out in all patients. Seventeen of the patients with chronic renal failure had clinically overt cardiovascular disease. Forty-five age-matched healthy subjects were considered as controls. 3. Both serum selenium concentration and platelet glutathione peroxidase were significantly reduced in all patients with chronic renal failure compared with control subjects; a direct and significant correlation was found between the two parameters. No differences in selenium status were observed among the non-dialysed, haemodialysis and continuous ambulatory peritoneal dialysis groups. No correlation between total calorie or protein intakes and selenium indices were observed. The chronic renal failure patients with cardiovascular complications showed a further significant reduction in both serum selenium concentration and platelet glutathione peroxidase activity as compared with the patients without cardiovascular complications; these two groups were similar with respect to the other well-known cardiovascular risk factors (age, smoking, plasma lipids, hypertension, body mass index). 4. It is concluded that a low selenium concentration is present in chronic renal failure, which is independent of dialysis and is accompanied by biological repercussion in terms of reduced platelet glutathione peroxidase activity.(ABSTRACT TRUNCATED AT 250 WORDS)