Heart rate variation is dependent upon an intact vagus nerve. Inherent beat-to-beat variability is expressed statistically as the mean square successive difference. Sinus arrhythmia is expressed as the standard deviation of the RR intervals. 19 normal volunteers and 19 nondiabetic hemodialysis patients were assessed for cardiac vagal innervation by monitoring heart rate variation on resting electrocardiograms. Comparison of the dialysis subjects with the normal individuals revealed significantly less heart rate variation in dialysis patients (p less than 0.01) consistent with abnormal cardiac vagal innervation. Measurement of resting heart rate variation allows assessment of the integrity of cardiac vagal innervation in normal individuals and nondiabetic patients with end-stage renal disease treated with intermittent hemodialysis.