Chicken eggs were treated with cyclopamine or jervine, either by yolk‐sac injection or application through windows made in the shell. Both methods resulted in a high mortality rate. No significant increase in the frequency of malformations resulted from yolk‐sac injection, but did occur after application of the compounds using windowed eggs. Retarded growth and development was also observed. Treatment with jervine at 14–28 h of incubation produced a high frequency of head malformations, but treatment later than this did not. Treatment with jervine at 30–40 h of incubation produced a high frequency of abnormalities other than head abnormalities, especially lordosis and rachischisis, whereas treatment before 28 h did not have this result. The frequency of head anomalies in the 16–28 h treatment groups was 30–60%, and the incidence of other anomalies in the 30–40 h treatment groups was 30–65%. Head abnormalities observed were cebocephaly, cyclopia, hydrocephalus, microphthalmia, meningocele, and encephalocele. Trunk and limb deformities were hemimelia, amelia, lordosis, and rachischisis. It was concluded that cyclopamine and jervine have a direct teratogenic effect on chick embryos. It appears that these compounds produce head malformations in chick and sheep embryos when they are exposed relatively at about the same developmental stage.