Golden hamster fetuses were extremely sensitive to the teratogenic action of jervine and cyclopamine, the steroidal alkaloid teratogens from Veratrum cali-fornicum. Cebocephaly, harelip/cleft palate, exencephaly, and a cranial bleb 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 dosing produced no terata. Swiss Webster mice were apparently resistant to the teratogens.