The aim of the present study was to find the answer was sought to following question: 1. is the superoxide anions release by lymphocytes after zymosan or phorbol myristate acetate stimulation elevated in patients with chronic renal failure?; 2. are there differences in superoxide anions release between groups of patients with chronic renal failure treated conventionally and those treated by haemodialysis? and 3. does dialysis with cuprophan membrane influence superoxide anions release in patients with chronic renal failure? 36 patients with chronic renal failure and 23 healthy subjects (control) were observed. All patients were divided in 2 groups: 1.12 patients conventionally treated (group 1) and 2.24 patients treated by haemodialysis (group 2). The subjects were studied in the early morning, after eight hour rest and in supine position. In patients of the group 2 blood samples were drawn immediately before and after haemodialysis. In all patients of the group 2 non-reutilized cuprophan dialysers and acetate buffer were used. In patients of the group 1 and in the controls blood samples were withdrawn only once. From the blood samples lymphocytes were isolated and stimulated by zymosan or phorbol myristate acetate. Superoxide anions release was measured using Babior method. Statistical analysis was performed using ANOVA test. A 95% confidence limit (p < 0.05) was used. O2.- release by lymphocytes in patients with chronic renal failure after zymosan (29,.1 +/- 1.0 nmol/min/10(7) lymphocytes) as well as phorbol myristate acetate (29.9 +/- 0.9 nmol/min/10(7) lymphocytes) was significantly higher than in healthy subjects (19.8 +/- 0.4 nmol/min/10(7) lymphocytes and 20.0 +/- 0.4 nmol/min/10(7) lymphocytes respectively).(ABSTRACT TRUNCATED AT 250 WORDS)