We investigated electrocardiographic changes occurring after hemodialysis in 20 male patients with chronic renal failure, changes in the configuration of T wave, ST segment and R wave consistent with ischemia were found in 30, 45 and 75%, respectively. Contrary to prior speculation the R wave height did not vary with the volume changes of body fluid occurring in dialysis. It is concluded that ischemic-appearing changes of uncertain significance are common in the postdialysis population.