To clarify the role of chronic anaemia in the pathogenesis of the left ventricular hypertrophy (LVH) of chronic uraemia, nine normotensive dialysed patients were studied before and 3 and 6 months after start of intravenous treatment with recombinant human erythropoietin (rHuEpo). M-Mode echocardiographic estimations of left ventricular mass indices (LVMi) and plasma noradrenaline determinations were made at 3 and 6 months, and total blood volume (TBV) only at 6 months. Resting haemoglobin values were 5.9 +/- 1.3 (SD) g/dl, increased within 3 months to 10.2 +/- 1.2 (P less than 0.001), then remained unchanged. Baseline LVMi was 115 +/- 18 g/m2 body surface area (b.s.a.) and decreased significantly (P less than 0.0025) over the entire period to a final value of 78 +/- 13 g, which did not differ from the average value for 19 healthy controls. Resting plasma noradrenaline was 1.45 +/- 0.44 pmol/ml and did not change significantly, although values were reduced at the 3rd month, when decreased heart rates and slightly and non-significantly increased blood pressures were recorded. TBV did not vary because the increased erythrocyte mass was compensated for by parallel decreases in plasma volume. These data demonstrate the existence of a cause-effect relationship between uraemic anaemia and LVH, although the precise mechanism remains unknown. Amelioration of anaemia with rHuEpo, by allowing recovery from the attendant LVH, might improve long-term cardiovascular prognosis in some dialysed uraemic patients.