We studied in 32 patients on maintenance hemodialysis (duration of treatment 6 to 133 months) whether duration of dialysis treatment affects blood pressure, plasma noradrenaline levels and alpha 2-adrenoceptor density (assessed in platelet membranes by 3H-yohimbine binding). Plasma noradrenaline levels were a significant inverse correlation to platelet alpha 2-adrenoceptor density. In addition, mean arterial blood-pressure, plasma noradrenaline levels and platelet alpha 2-adrenoceptor density were significantly related to the duration of treatment: with increasing duration of treatment plasma noradrenaline levels increased, whereas mean arterial blood-pressure and platelet alpha 2-adrenoceptor density decreased. Furthermore, changes in mean arterial blood-pressure were inversely related to plasma noradrenaline levels and positively to platelet alpha 2-adrenoceptor density. Platelet alpha 2-adrenoceptor changes were accompanied by similar alterations in (vascular) alpha 1-adrenoceptor responsiveness (assessed by blood pressure responses to i.v. injections of phenylephrine); in hypotensive hemodialysis patients, who had high, plasma noradrenaline levels and low, platelet alpha 2-adrenoceptor density, the dose of phenylephrine necessary to increase systolic blood pressure by 20 mm Hg was nearly twice as high as in normotensive dialysis patients and healthy controls. In autonomic tests, Valsalva-ratio was lower in hypotensive than in normotensive dialysis patients and healthy controls, whereas no differences were found in blood pressure and heart rate responses during sustained hand-grip exercise as well as in beat-to-beat variation during deep breathing.(ABSTRACT TRUNCATED AT 250 WORDS)