The effect of parathyroidectomy on left-ventricular function was evaluated in chronic-haemodialysis patients with advanced hyperparathyroidism. Radionuclide angiocardiography (22 patients) and ultrasound echography (8 patients) revealed a significant increase in left-ventricular ejection fraction 1--2 weeks after parathyroidectomy. This improvement was associated with an augmented cardiac index (radionuclide method) and with an increase in mean velocity of circumferential myocardial fibre shortening (echocardiography). Circulating blood volume and erythrocyte space, as well as arterial blood-pressure, had changed little after parathyroidectomy, whereas plasma calcium, phosphate, and immunoreactive parathyroid hormone were significantly lower after surgery. Thus, correction of severe hyperparathyroidism led to a significant improvement in cardiac performance.