1. The effects of chronic administration of erythropoietin (EPO) on blood pressure and renal function in rats with ablation of renal mass were assessed. 2. Spontaneously hypertensive rat were subjected to 5/6 nephrectomy (5/6Nx). Four weeks after the operation, the rats were randomly allocated to vehicle, EPO 20IU/kg i.p., or EPO 100 IU/kg i.p. (both given twice a week) for 4 weeks. 3. Marked anaemia was noted in SHR-5/6Nx. EPO caused a significant increase in haematocrit at a high dose but not at a low dose. A dose dependent relationship was noted in the EPO-induced rise in the systolic blood pressure. 4. EPO dose-dependently increased urinary protein excretion. It also increased blood urea nitrogen and serum creatinine levels. 5. These results suggest that EPO ameliorates anaemia and severely accelerates renal failure in SHR-5/6Nx. They also suggest that anaemia can be a haemodynamically favorable adaptation to chronic renal disease and that its correction may have adverse renal haemodynamic and structural consequences.