The environmental contaminant cadmium (Cd) is a proven teratogenic agent in rodents. In hamsters, it causes craniofacial dysmorphogenesis. The underlying mechanism for this damage is unknown. Early facial development in hamsters occurs during gestation days 9-11 and involves the formation and appropriate fusion of several prominences surrounding the stomodeum. The hypothesis for this study is that the occurrence of Cd-induced facial defects involves a disruption of the normal formation and/or fusion of one or more of the facial prominences. Pregnant hamsters were treated with Cd (2 mg/kg) or water intravenously on gestation day 8 (8 A.M.). On gestation day 10 (8 A.M.) surviving embryos were processed to obtain scanning electron micrographs of the frontal view of the face. Measurements of the surface areas of 15 different portions of the face were obtained using a microcomputer equipped with a digitizer. Both qualitative and quantitative differences in the faces were detected upon comparing the Cd-exposed and control embryos. The surface areas of the prominences measured were significantly smaller in the Cd-exposed embryos. However the sizes of the other regions of the Cd-exposed faces were either little affected (nasal pit areas) or markedly increased (the interval of the face between the medial nasal prominences). Two possible explanations for these data are discussed.