LBO0014, a new recombinant human erythropoietin, was at dose levels of 0, 120, 600, and 3,000 IU/kg/day administered intravenously to pregnant Sprague-Dawley rats during the organogenetic period. All dams were subjected to caesarean section on day 20 of pregnancy, Effects of test substance on dams and embryonic development of Fl fetuses were examined. No treatment-related changes in clinical signs, body weight, and food consumption were observed at all doses tested. At necropsy spleen enlargement was found at 3,000 lU/kg. There was an ulcrease in the spleen weight at 600 and 3,0007/kg. Developmental toxicity was evident as increased resorptions at 3,000 lU/kg. At 600 and 3,000 RJ/kg, retarded ossification of fetuses occurred at an incidence of 31.3% and 64.7%, respectively. In addition, there was a delay in ossification of sternebrae and sacrocaudal vertebrae at 600 and 3,000 lU/kg. A decrease in the number of metacarpi and metatarsi was also seen at 3,000 nJ/kg. The results show that the no observed adverse effect dose level (NOAEL) for material toxicity was over 3,000 IU/kg/day and the NOAEL for developmental toxicity was 120 IU/kg/day.