The cardiovascular responses to the Valsalva manoeuvre and sustained handgrip were measured in 26 patients with chronic renal failure treated with intermittent haemodialysis. Twelve (50%) had an abnormal Valsalva response and ten (45%) had an abnormal handgrip response. There was a reduction in the beat-to-beat variation of heart rate at rest in those patients who had abnormal Valsalva manoeuvres, independent of age or the resting heart rate. It is concluded that autonomic nerve fibres may be damaged in patients with chronic renal failure on intermittent haemodialysis in the absence of symptoms of autonomic neuropathy. These studies suggest three simple ways of testing autonomic function in haemodialysis patients which could routinely be performed to detect patients at risk of developing an abnormal reaction to volume depletion during haemodialysis.