Eight patients with chronic renal failure before the stage of dialysis (Group 1), 11 patients on regular dialysis treatment (Group 2) and 14 healthy control subjects (Group 3) were studied before, during and after angiotensin II (AII)-infusion. Blood pressure (BP), heart rate (HR), plasma levels of AII, aldosterone (Aldo), arginine vasopressin (AVP), noradrenaline (NA) and adrenaline (A), and serum concentrations of parathyroid hormone (PTH), calcium and magnesium were determined. AII induced vascular reactivity was reduced both in Group 1 and 2 compared with Group 3. Basal AII was the same in the three groups, and only in dialysis patients was AII induced vascular reactivity negatively correlated to basal AII. Aldo and NA were higher in Group 2 than in Group 3, and AVP was higher in both groups of patients compared with controls. HR declined during AII induced elevation of BP in the control subjects but not in the patients. Neither PTH, serum calcium nor serum magnesium was correlated to BP or vascular reactivity. It can be concluded that AII induced vascular reactivity is reduced both in patients with renal failure before dialysis and in patients on regular dialysis treatment. Basal blood levels of Aldo and NA are increased in dialysis patients and AVP is increased in both groups of patients, but neither these abnormalities nor blood levels of PTH, calcium or magnesium seem to be the background upon which the abnormal vascular reactivity develops.