Ochratoxin A (OA), a mycotoxin commonly found in soils and on moldy food such as cereal grains, is a potent teratogen. The present investigation was designed to examine the teratogenicity of OA administered acutely at early post-implantation stages in mice, with particular emphasis on the pathogenetic basis of induced malformations. Maternal OA administration on gestational day (GD) 7 or 8 resulted in excessive amounts of cell death in selected cell populations. After a single dose of 2-4 mg/kg, excessive cell death was notable within 6 hours, and persisted to 36 hours post-treatment. As observed in GD 14 or 18 fetuses, the spectrum of induced craniofacial malformations included exencephaly, midfacial clefting, cleft lip, as well as hypotelorism, and synophthalmia associated with holoprosencephaly. Body wall defects involved either the abdominal wall alone, or in combination with the thoracic wall, resulting in partial or complete exposure of the viscera. Potential mechanisms for OA-induced selective cell killing are discussed.