A teratogenicity study was carried out on Sprague-Dawley rats which have been given the intravenously or intraperitonealy injections of rHuIFN-${alpha}$A, an available therapeutic agent, at dose levels of $1{ imes}10^5$, $4{ imes}10^5$ and $1.2{ imes}10^6$ I.U/kg/day for a period of 11 days from day 7 to day 17 of gestation. Two-thirds of the pregnant females in each group were sacrificed on day 20 of gestation and their fetuses were examined. The remaining dams were allowed to litter naturally, and the postnatal development of the off springs was observed. No changes were observed in all aspects of parameters between the treated and the control dams. The incidence of external, internal, and skeletal anomalies were not significantly increased in the fetuses of any treated groups. The rHuIFN-${alpha}A$ caused no effects on parturition, lactation, and postnatal growth.