Golden hamster fetuses were extremely sensitive to the teratogenic action of jervine and cyclopamine, the steroidal alkaloid tetratogens from Veratrum californicum. Cebocephaly, harelip/cleft palate, exencephaly, and a cranial bled were the common deformities produced by dosing on the seventh day of gestation. Sprague-Dawley derived albino rats were susceptible to cyclopamine but not to jervine, and at an incidence very much lower than that of hamsters. Cebocephaly and microphthalmia were the common deformities. The terata were observed as a consequence of sixth to ninth-day dosings. Single-day dosings produced no terata. Swiss Webster mice were apparently resistant to the teratogens.