Induction of DNA fragmentation of rat embryonic midbrain cells was studied to see whether apoptosis plays a role in OTA-induced microcephaly observed in cultured rat whole embryos during embryogenesis. We first cultured whole embryos (prepared from day 9.5 gestation rats) for 48 hrs with OTA and found that OTA induced microcephaly in cultured rat whole embryos. We also examined whether the microcephaly seen in cultured whole embryos is partially related to the increase of apoptosis of undifferentiated embryonic midbrain cells. Embryonic midbrain cells were prepared from day 12 gestation rat embryos, and cultured in the mixture media of Dulbecco's modified eagle's medium nutrient and Ham's F12 (1 : 1) containing 10% Nuserum, 100 ㎍/㎖ of streptomycin and 100 units/ml of penicillin for 96 hrs. Induction of DNA fragmentation was increased by 0.25-1 ㎍/㎖ OTA in a dose dependent manner in the embryonic midbrain cells. We also tested whether increase of apoptosis by OTA would be associated with change of apoptosis-related proteins (TNF-α and P^(53)) level in embryonic rnidbrain cells. OTA also increased TNF-α and P^(53) levels. These results show that OTA induced microcephaly in cultured whole embryos and this effect may be at least a part due to the induction of apoptosis and apoptosis-related protein levels of undifferentiated embryonic midbrain cells.