The effects of fumonisin on development of Syrian hamster fetuses were studied using fumonisin B1 and B2 extracted from Fusarium moniliforme corn-culture and purified fumonisin B1. A significant increase in litters with fetal deaths occurred with the high doses of purified (18 mg FB1/kg) and culture-extracted (18 mg FB1 plus 4.5 mg FB2) fumonisin. It is concluded that prenatal exposure to fumonisin on days 8 and 9 of gestation is detrimental to fetal hamster survivability but does not induce clinical maternal intoxication at these doses. Equivalent doses of fumonisin B1, whether from culture-extract or pure solution produced similar results.