Efficacy and in vivo bioassay of recombinant human erythropoietin (rho-EPO), was investigated. Efficacy studies were conducted in normal, and cisplatin-induced anemic rats. Normal and anemic animals were treated intravenously with rhu-EPO for 5 days, and the changes in the number of red blood cells (RBC), hemoglobin concentration (Hb), hematocrit value (Hct) and percentage reticulocyte value (Ret, reticulocyte/RBC) were examined. In normal rats, rho-EPO significantly increased RBC, Hb, Hct and Ret at the doses of 50∼ 1,250 lU/kg/day in a dose-dependent fashion. Cisplatin-induced anemic rats showed significant increase of RBC, Hb, Hct and Ret after administration of rho-EPO (50-200 lU/kg/day) in a dose-dependent manner. These changes of hematological parameters disappeared gradually after cessation of the treatment. The in vivo bioassay results in polycythemic mice showed that rho-EPO had 90% of bioactivity compared to NIBSC standard rhu-EPO. These results suggest that rho-EPO might be useful for the therapy of anemia originated from renal failure and chemotherapy-induced anemia.