THE concern about the psychological and physiological effects of lysergic acid diethylamide (LSD) has naturally led to the desire for experimental models to study the spectra of effects suspected to be caused by LSD. Among the recent reports of its biological effects when pregnant animal models are used, one involving rats is negative1, another2 is ambiguous because although stunted and stillbirths were reported with LSD at 10 days post partum the offspring were unusually large, weighing 44–46 g. Results with hamsters3 are equivocal because of the small incidence of malformations reported, and those for mice are positive4.