α1-Adrenoceptor Junction and plasma catecholamine levels were investigated in chronically hemodialyzed patients with and without hemodialysis-induced hypotension. In the interdialytic period blood pressure responses as well as the mydriasis after topical application of theα1-selective agonist phenylephrine were not significantly different in patients with or without hypotension during dialysis, although patients with hypotension were more susceptible to miosis induced by the muscarinergic agonist carbachol. In the normotensive group the blood pressure increasing effect of phenylephrine was attentuated after 120 win of hemodialysis therapy. Plasma noradrenaline levels were not significantly different in both groups and did not change significantly during hemodialysis, while plasma dopamine was significantly increased in the hypotensives. Thus, evidence for a pathophysiological role of a postsynapticα-adrenoceptor dysfunction in hemodialysis-induced hypotension was lacking.