We assessed standard 12-lead and Holter electrocardiographic (ECG) abnormalities in maintenance hemodialysis (HD) patients. Of 221 outpatients receiving HD, 143 (65%) had ECG abnormalities. Rates were higher in male, elderly, hypertensive, and diabetic patients than in female, younger, normotensive, and nondiabetic patients. The prevalence of ECG changes correlated inversely with HD duration. Serial ECGs were compared in 87 patients whose average HD duration was 7.5 +/- 2.5 years. Thirty-four patients (39%) showed normal ECGs throughout, 27 (31%) relatively stable abnormalities, 22 (25%) worsening, and 4 (5%) reversion to normal. Age, hypertension, and diabetes are factors related to abnormal ECG findings. Among the 142 Holter recordings from 72 patients, 70 (97%) were basically in sinus rhythm, and 2 (3%) were in atrial fibrillation. The average frequency of supraventricular premature contractions (SVPCs) was 1597 +/- 9725 per 24 hours, and that of ventricular premature contractions (VPCs), 556 +/- 1415. VPCs were multifocal in 9%, in runs in 25%, and early in 1%. In 29 (40%) of recordings, VPCs appeared mainly during and for several hours after HD. ST-T changes were seen in 43 (60%). In 11, ST depression occurred during and a few hours after HD. Patients receiving HD showed diverse ECG abnormalities. Holter ECGs revealed a high incidence of arrhythmias and ST-T changes, which frequently appeared in relation to HD timing.