LBD-005, a newly developed recombinant granulocyte-macrophage colony-stimulating factor, was at dose levels of 0, 20, 80 and 320ng/kg/day administered subcutaneously to pregnat New Zealand White rabbits during the organogenetic period. The dams were subjected to caesarean section on day 28 of pregnancy. Effects of test substance on dams and embryonal development of fetuses were examined. No treatment-related changes in clinical signs and necropsy findings of dams were observed in all groups. At 80 and 320 ng/kg, a significant decrease in food consumption followed by a loss in body weight was found.