Cardiac arrhythmias were evaluated in 20 patients (14 males and 6 females; 38.2+/-17.6 years) undergoing regular maintenance hemodialysis (HD) for chronic renal failure (CRF) by Holter ECG monitoring a 24-hour period. Ventricular arrhythmias (VAs) were observed in 18 of 20 patients (90%). Sporadic VAs were recorded in 75% and frequent VAs in 15% of 20 patients. It was found that VAs were correlated with an increase in duration of CRF, but there was no relation with age, duration of HD, frequency of HD, body surface area, the levels of serum sodium, chloride, creatinine, phosphorus (P), magnesium, free calcium (Ca), and free fatty acids, CaxP, cardiothoracic ratio, ejection fraction, fractional shortening, interventricular septum thickness, left ventricular posterior wall thickness, left ventricular end-diastolic dimension and left ventricular end-diastolic index. VAs recorded frequently during HD and for 4 hours after HD. In addition, sporadic supraventricular arrhythmias (SVAs) were observed in 16 patients (80%) and frequent SVAs were recorded in 2 patients (10%).