The effect of recombinant human erythropoietin (rHmEPO) on lymphocytic phenotyping as well as on the phagocyte activity of polymorphonuclear cells and monocytes was evaluated in 16 patients on maintenance hemodialysis. The mean age of the patients was 38.2 +/- 16.2 years. There were seven men and nine women. All patients were started on 50 U/kg of rHmEPO intravenously three times per week, and the dosage was increased gradually to achieve target haemoglobin of 12 g/dL. Predialysis blood samples were taken monthly for 3 months, and phagocyte respiratory burst as well as lymphocyte subsets were studied. Healthy blood donors were taken as controls. By 3 months of rHmEPO treatment, there was no significant increase in total T and B cells, but there was a significant increase in both CD4 (P < 0.001) and CD8 (P < 0.005): however, there was no significant change in the CD4/CD8 ratio. There was significant reduction in the natural killer cells (P < 0.005). The phagocyte activity studies showed a significant increase in the respiratory burst in whole blood (P < 0.001) and opsonized zymosan (P < 0.001) as well as improvement in the suppressed polymorphonuclear cell and monocyte activity by uremia. Phagocytosis studied by yeast uptake showed significant improvement from the pretreatment suppressed phagocytes to normal activity posttreatment. In conclusion, treatment with rHmEPO increases CD4 and CD8 cell counts without affecting the CD4/CD8 ratio, decreases the natural killer cells, and improves the impaired phagocyte activity in hemodialysis patients.