AbstractThe embryotoxic properties of an ethanol extract of boiled potatoes infected withPhytophthora infestanswere investigated in White Leghorn chicken embryos, using controlled subgerminal injection on the second day of incubation and intraamniotic injection on the third and fourth days. A dose of 0.3 mg of sublimation‐dried extract interfered at the somite stages with the function of the caudal morphogenetic system and induced various degrees of the caudal regression syndrome. Administration on the third and fourth days led to the development of a malformation syndrome comprising cranioschisis, celosoma, and cardiac septal defects. An equivalent amount of extract of healthy potatoes of the same variety and injection of pure solanine had the same effect. The results warrant the claim that the main factor responsible for the direct embryotoxicity of potatoes attacked byP. infestansis solanine, which evokes tonic contract ion of the smooth muscle elements of the amnio