GRg1 is one of the most important active agents extracted from ginseng. Although there are numerous reports in the medical literature concerning the beneficial effects of GRg1, little is known about its effects on embryonic development. In our study, whole embryo culture was applied to explore the effects of GRg1 on SD rat and ICR mouse embryos during their critical period of organogenesis. All embryos were exposed to different concentrations of GRg1, and scored for their growth and differentiation at the end of the 48-h culture period. Total morphological score decreased significantly at the concentration of GRg1 of 50 microg/ml to mice and at 30 microg/ml to rats. The whole embryonic growth was affected, represented as reduced crown-rump length and head length, and decreased number of somites from 10 microg/ml both in mice and rats. Morphological development was influenced relatively late. To rats, the scores of flexion, forelimb bud and hindlimb bud were significantly reduced at 30 microg/ml, and heart was among the affected organs. However, the effect on heart was not observed in mice, and flexion and limb buds were influenced at 50 microg/ml. These results demonstrate that GRg1 has embryotoxicity during both rat and mouse organogenetic period and rats might be more sensitive than mice. We suggest that pregnant women of first trimester should use ginseng with caution before the exact conclusion is obtained.