Petroleum ether extracts of panax ginseng C.A. Meyer (GPEE) were tested for the evaluation of anticlastogenic effects against benzo(a)pyrene-induced micronucleated polychromatic erythrocytes using mouse bone marrow micronucleus test. When the GPEE was singly administered before benzo(a)pyrene injection, GPEE showed significant anticlastogenic effect at $50{sim}200;mg/kg$. When the GPEE was multiply administered for 5 consecutive days before benzo(a)pyrene injection, GPEE showed potent anticlastogenic effect, even at the low doses, $5{sim}50;mg/kg/day$. As a control experiment, GPEE was administered without benzo(a)pyrene injection to demonstrate a clastogenic effect of this extract. When the range of $1{sim}200;mg/kg/day$ for 5 consecutive days was administered to mice, it was found that there was no increase of MNPCEs frequency.