Using the Holter method, the authors monitored for 24-hours 30 patients included in a long-term dialyzation programme during and after haemodialysis. A group of 15 patients who had during examination frequent or complex supraventricular or ventricular ectopia was compared with a group of 15 patients with sporadic ectopia. In the arrhythmic group paroxysmal supraventricular tachycardia was recorded in 33% and paroxysmal atrial fibrillation in 13%, polytopic or repetitive ventricular extrasystoles in 14%, couplets in 20% and volleys of ventricular extrasystoles or non-persisting ventricular tachycardia in 20%. Comparison of clinical laboratory and echocardiographic characteristics revealed in the arrhythmic group significantly higher mean ages of patients, higher levels of ionized serum calcium before haemodialysis, C terminal parathormone, the breadth of the interventricular septum, and the authors observed also a higher incidence of hyperechogenity of cardiac structures. On analysis of repolarization ECG changes significant asymptomatic depressions of the ST segment were found which were transient and dominated during the early posthaemodialyzation period in 11 patients of the whole group (37%).