Autonomic function was studied in 46 hemodialysis (HD) patients (aged 19-62 years, 30 men and 16 women), eight continuous ambulatory peritoneal dialysis (CAPD) patients (aged 29-78 years, five men and three women), and 107 normal adults (aged 21-80 years, 63 men and 44 women) by noninvasive cardiovascular reflex tests. The autonomic function tests included heart rate (HR) response to standing up, during the Valsalva maneuver, deep breathing and diving, and blood pressure response to standing up, during immersion of the hand in ice water, and during a sustained handgrip. The Master 2-step exercise test was also performed in HD patients and in normal controls. The results showed that: 1) HD patients had a significantly smaller R-R interval 30:15 ratio (1.04 vs 1.19), Valsalva ratio (1.27 vs 1.45), and HR change during diving (8.7 vs 19.2) than normal controls; 2) both the 30:15 ratio (1.00) and Valsalva ratio (1.19) in CAPD patients were significantly smaller than those in controls; and 3) the rate pressure product at three minutes for HD patients was significantly greater than that of normal controls (27060 vs 21300). In conclusion, dialysis patients revealed abnormalities in the cardiovascular autonomic function tests, especially in the parasympathetic tests. Exercise intolerance was also evident in these patients.