Hemodialysis patients, nondialyzed azotemic patients and control subjects with chronic physical disabilities were tested in psychometric measures of attention, memory, and visuomotor speed and coordination. There was relatively little difference between the performance of dialysis patients and controls and no significant correlations were found between years of dialysis treatment and performance on any task. In contrast, nondialyzed azotemic patients were impaired on 9 of 14 tasks relative to controls and/or dialysis patients. Measured levels of blood urea nitrogen (BUN) and serum creatinine were significantly correlated with the performance of nondialyzed azotemic patients on several tasks. These results demonstrate a relationship between degree of renal failure and cognitive and perceptual-motor functioning. The mild impairments evident in dialysis patients do not seem to be directly attributable to dialysis treatments. Rather, the onset of hemodialysis appears to have beneficial effects on neuropsychological function.