Pituitary-adrenocortical axis is disturbed in patients with chronic renal failure. Such abnormalities have been described in diabetic patients, too. The studies were performed to answer the following questions: 1) Is there a difference in basal ACTH and cortisol plasma level between patients with diabetic nephropathy and normal subjects? 2) Does haemodialysis affect ACTH and cortisol plasma level in patients with diabetic nephropathy? 18 patients with diabetic nephropathy and 10 normal controls were the subjects of this study. Blood samples for ACTH and cortisol determination were collected from each patient with diabetic nephropathy four times: before haemodialysis from the arterial line of dialyzer (0a) after 60 minutes of haemodialysis from the arterial (60a) and the venous (60v) line of dialyzer and after 240 minutes of haemodialysis from the arterial line (240a). Blood samples from normal controls were collected at 6 a.m. to determine ACTH and cortisol level. All the diabetic patients were on chronic 4-hour-haemodialysis 3 times a week. An artificial kidney Fresenius 4008 E, polysulfone dialyzers F5 and acetate dialysing solution were used in the studies. Plasma samples were analyzed for cortisol and ACTH by RIA. The studies brought to following conclusions: 1) The basal ACTH plasma level is significantly higher in patients with diabetic nephropathy than in normal controls. There is no significant difference in cortisol plasma level between diabetic patients and the control group. 2) Haemodialysis effects significant decrease of ACTH in plasma of diabetic patients. There is no statistic significance in cortisol plasma level in diabetic patients during haemodialysis.