A series of experiments was performed to clarify the role of androgens in the development of sex differences in the acquisition of active avoidance behavior. Gonadectomy in adulthood did not affect the performance of either sex regardless of the length of the postoperative recovery interval. Neonatal castration also failed to improve the avoidance performance of males, but prenatal exposure to the antiandrogen cyproterone acetate combined with neonatal gonadectomy produced males whose avoidance acquisition and open field activity scores were indistinguishable from those of control females. Prenatal exposure to endogenous of normal males, but there is no compelling evidence that exposure to androgens during the prenatal period is critical to this effect.