The pharmacological responses produced by alpha chaconine and tomatine on guinea pig ileum, on the isolated electrically stimulated frog ventricle, and recordings of EEG, ECG, respiration and blood pressure in the rabbit showed no essential differences from those produced by alpha solanine. The LD50 values of chaconine and solanine in the mouse and rabbit are also similar and suggest that compounds other than these are probably responsible for the predominant toxic effects of certain hybrid potatoes in man and animals. The failure of the three glycoalkaloids to produce a significant teratological effect in the chick embryo lends no support to the hypothesis that they may be the teratogens responsible for certain congenital malformations in man.