PIP: Keeping as many variables as possible constant, several indices of reproductive function were examined in female rats androgenized by different methods. The age at which vaginal opening occurred, the incidence of persistent estrus, the ovarian, uterine, adrenal, and pituitary weights, and the pituitary and serum gonadotropin (FSH, LH, prolactin) concentrations were compared in female rats treated neonatally with 10 mcg estradiol benzoate (EB), 250 mcg androstenediol-propionate, 250 mcg dehydroepiandrosterone (DHEA) or 10, 50, 250, or 1,250 mcg doses of testosterone propionate (TP). The animals were treated with EB and TP at 5 days of age, and they were killed at 40, 90, and 150 days of age. By 90 days of age, 99% of the rats treated with steroids other than DHEA were in constant estrus. None of the rats given DHEA became anovulatory. In all anovulatory females, the pituitary prolactin content increased with age, and it was higher than in animals given DHEA. Serum prolactin was linearly related to both the dose of TP given and the animal's age. The findings appear to support the belief that loss of prolactin-inhibiting control mechanisms of the hypothalamus is a consequence of aging. It is not known whether this is related to a loss of neurons or only to a loss of function.