The subchronic toxicity study of rHuEPO, a newly developed recombinant erythropoietin, was investigated for 13 weeks in Beagle dogs intravenously treated with doses of 100, 500 and 2,500 lU/kg/day. There were no significant changes in body weight, food intake, physical and opthalmic examination, urine analysis, etc. Any toxic response was not observed except for enlarged spleen and extramedullary hematopoiesis. These results indicate that the no-observed adverse effect level (NOAEL) of rHuEPO is 100 lU/kg in Beagle dogs.