AbstractAlthough the embryopathic effects of caffeine have been established in various mammals little is known about the mechanisms involved. Speculating that caffeine teratogenicity may be linked to catecholamine release induced by this compound we attempted a prophylactic type of experiment against caffeine teratogenicity in mice by maternal pretreatment with propranolol, a β‐adrenergic‐blocking agent. Pregnant mice on day 13 of gestation were each given a single iv injection of 2.5, 5. or 10 mg/kg propranolol and five minutes later a single ip injection of 200 mg/kg caffeine. The controls received saline or either of the drugs alone. Fetuses were examined for abnormalities on day 19 of gestation. The fetoputhic effects of caffeine were significantly reduced by pretreatment with propranolol at all dosages; and it was therefore hypothesized that the β‐adrenergic actions of catecholamines caused to be released by caffeine induce fetal circulatory disturbance, which leads to fetal abnormalities.