YHB6211, a newly developed recombinant human granulocyte colonystimulating factor, was administered at dose levels of 0, 3, 15, and 75 $mu$g/kg/day intravenously to the pregnant New Zealand White rabbits (20 rabbits per group) during the organogenetic period, days 6 to 18 of gestation. All dams were subjected to Caesarian section on day 28 of gestation and their fetuses were examined for external, visceral, and skeletal abnormalities. No abnormalities in clinical signs, body weight changes, gross findings, mortality, and external appearance were found in all dams and fetuses exposed to 0, 3, and 15 $mu$g/kg/day of YHB6211. However, in the group treated with 75 $mu extrm{g}$/kg/day of YHB6211, maternal body and uterine weights, fetal body weights and length, and the number of live fetuses were significantly decreased and further fetal mortality was remarkably increased. It is suggested that YHB6211 may have no side effect up to the dose level of 15 $mu$g/kg/day, and there would be no teratogenicity for fetuses of rabbits up to 75 $mu extrm{g}$/kg/day even if it may have some toxic effects over 75$mu extrm{g}$/kg/day for dams and fetuses of rabbits.