In eleven patients with uraemia on intermittent haemodialysis treatment, recombinant human erythropoietin (rHuEpo) was used at a dosage schedule of 100 IU/kg bodyweight thrice weekly. Erythrokinetic studies (blood volume, RBC survival and iron kinetics) were performed in nine cases before and after 6 months of treatment. The remaining two patients had only RBC and plasma volume determinations before and after treatment. Although total blood volume remained unchanged, RBC volume was increased in all cases. Red cell loss was not modified, and quantitative improvement of RBC production was noted in all cases. No qualitative defect of erythroid maturation or release was observed in the treated patients. In conclusion, rHuEpo treatment improves the anaemia of haemodialysis patients by normalising circulating RBC volume only through an increase in red cell production.