Laetrile administered orally ot pregnant hamsters caused skeletal malformations in the offspring, but intravenous laetrile filed to result in embryopathic effects. Oral laetrile significantly increased in situ cyanide concentrations, while intravenous laetrile did not. Thiosulfate administration protected embryos from the teratogenic effects of oral laetrile. The embryopathic effects of oral laetrile appear to be due to cyanide released by bacterial beta-glucosidase activity.