The effects of alkylation agent mustarnitrogen on correlation between postimplantation fetal mortality and lipid peroxidation activities in pregnant female Wistar rat liver and embryos homogenates thereof were studied. Mustarnitrogen (0,4 mg/kg) was administered on day 10 of pregnancy to rat tail vein. It was shown the increased rate of TBA-active products formation on day 20 of pregnancy in female liver and embryos to be 3,5- and 2,7-fold, respectively, as compared to intact animals. The level of postimplantation fetal mortality was 4-fold higher, than that of intact animals. The direct correlation between activation of lipid peroxidation in pregnant rat and postimplantation fetal mortality (R=0,7) was observed under the effect of alkylation agent. The administration of &-tocopherol derivatives during pregnancy normalized the level of lipid peroxidation in liver and embryos of pregnant females and decreased postimplantation fetal mortality. The data obtained allow to suggest that mustarnitrogen embryotoxicity, in addition to alkylation, is highly correlated with the activation of free-radical processes and demonstrate the possibility of decreasing alkylation agents toxicity by using antioxidants.