Fifty-two patients with terminal chronic renal failure on haemodialysis were assessed for the existence of autonomic neuropathy using the Valsava index. The values in the patients were lower than in the controls. Only a few symptoms could be related to the autonomic neuropathy. No correlation was found between Valsalva index and orthostatic or intradialysis hypotension, motor-nerve conduction velocity or plasma intact parathyroid hormone. Having demonstrated the existence of autonomic neuropathy, eight healthy subjects and ten patients on haemodialysis were studied to locate the segment of the autonomic reflex are affected. Heart rate and intraarterial pressure were monitored during the following tests: phenylephrine; hyperventilation; cold pressor; atropine; tyramine and adrenaline. An alteration was observed in baroreceptors, together with adrenergic hyperexcitability (reflected in the hypersensitivity of the sympathetic efferent pathway) and a greater response to the stimulus for the release of extra-adrenal adrenaline. The lower response to atropine is indicative of vagal alteration.