The effect of long-term treatment with human recombinant erythropoietin (rHuEPO) has been studied in nine end-stage renal disease patients on continuous ambulatory peritoneal dialysis (CAPD). RHuEPO was administered subcutaneously twice weekly in rising doses starting with 50 Ukg-1 body weight. After 3 months of rHuEPO haemoglobin increased from 77.7 +/- 3.2 to 112.7 +/- 5.6 g l-1 (P less than 0.03), haematocrit rose from 22.8 +/- 1.2 to 30.3 +/- 1.7% (P less than 0.01). A consistent decrease in ferritin concentration was observed during this time (P less than 0.05). After 12 months of rHuEPO treatment and increased oral iron supplementation the rises of haemoglobin and haematocrit remained stable without other significant haematological changes. The rHuEPO-induced rise in haematocrit was associated with an increased peritoneal ultrafiltration (UF) without change in diuresis and body weight. UF improved from 128 +/- 28 ml 4 h-1 dwell time to 273 +/- 45 ml 4 h-1 (P less than 0.03) within 3 months of rHuEPO treatment, and remained stable during the following study period (month 12: 253 +/- 43 ml 4 h-1, P less than 0.05). The rise in UF resulted in improved peritoneal clearances of creatinine, urea, potassium, and phosphate (P less than 0.05, month 3). No change was observed in serum urea, creatinine, calcium, and potassium. Serum phosphate increased throughout the first 6 months of rHuEPO (P less than 0.05). No severe adverse effects of rHuEPO treatment could be observed. The present results demonstrate that long-term subcutaneous administration of rHuEPO is effective in correcting renal anaemia in CAPD patients and may improve dialysis efficiency by increased peritoneal ultrafiltration.