The sexual behavior of male and female guinea pigs from mothers receiving testosterone propionate during most of pregnancy was studied after the attainment of adulthood. As a part of the investigation, the responsiveness of the females to estradiol benzoate and progesterone and to testosterone propionate was determined. The larger quantities of testosterone propionate produced hermaphrodites having external genitalia indistinguishable macroscopicalty from those of newborn males. Gonadectomized animals of this type were used for tests of their responsiveness to estradiol benzoate and progesterone and to testosterone propionate. The capacity to display lordosis following administration of estrogen and progesterone was greatly reduced. Male-like mounting behavior, on the other hand, was displayed by many of these animals even when lordosis could not be elicited. Suppression of the capacity for displaying lordosis was achieved with a quantity of androgen less than that required for masculinization of the exte...