Orciprenaline sulfate is a beta-adrenoceptor stimulant chemically described as 1-(3,5-dihydroxyphenyl)-1-hydroxy-2-isopropylaminoethane sulfate (Alupent®). The drug has broncho-dilating activity and has been developed in numerous countries since 1961. The purpose of these studies was to investigate the teratogenic potential of orciprenaline and its mode of action in pregnant Jcl:ICR mice, when administered during the period of organogenesis and, more systematically, during the critical period of palate formation. Daily doses of 5, 50, and 500 mg/kg were given orally by gavage to mice on days 6–15, 11–13, or on day 12 of gestation. Additional studies were done to evaluate the maternal cardiotoxic action of orciprenaline and its effects on adrenal cortex and endogenous serum corticosterone. Five mg/kg triamcin-olone acetonide, a glucocorticoid, were given subcutaneously as a positive control causing 100% cleft palate. Myocardial necroses occurred in pregnant mice only after 500 mg/kg orciprenaline had been given, and a significant increase in cleft palate occurred if exposure took place during days 11–13 or day 12 of gestation. This increase in cleft palate can be explained by the teratogenic effect of an elevated maternal serum corticosterone level 1 hr after orciprenaline treatment, about three times the control value.