The teratogenic potential of the anticonvulsant drug phenytoin (PHT) has been well documented both in the human and in the experimental animals. However there are few reports on the effects of PHT on embryonic development in rats in vitro. The present study was performed to evaluate the teratogenic effects of PHT using whole-embryo culture system in rats. Sprague-Dawley rat embryos were explanted on gestational day (GD) 9.5 and cultured for 48 hrs in the immediately centrifuged and heat-inactivated rat serum containing 0,25,50, or $100{mu}g$ PHT/mL. At the end of culture period the embryos were scored for morphological development according to the procedure of Van Maele-Fabry, and their total protein contents were determined. At 100 ${mu}$g/mL of culture medium. PHT caused significant reduction in developmental score and protein content of embryos and a high incidence morphological abnormalities (100%). Characteristic malformations included altered yolk and embryonic circulation, craniofacial hypoplasia, neural tube schisis, branchial arch defects, abnormal ratation, and limb bud hypoplasia, among others. There were no adverse effects on embryonic growth and development at concentrations of 25 and 50 ${mu}$g /mL of culture medium. The results indicated that the dysmorphogenic effect of PHT on cultured embryos is due to a direct interference with embryonic development.