Female ferrets that received injections of testosterone propionate (TP) early in postnatal life displayed significantly more masculine behavior than did control females when gonadectomized and administered either TP or estradiol benzoate in adulthood. This increased masculine response potential was not correlated with the effects of early TP treatment on phallic development. In contrast to results obtained in most other species, perinatal administration of TP to female ferrets failed to disrupt their ability to display the behavior that is characteristic of the sexually receptive animal in estrus. When estrogenic stimulation was provided in adulthood, the receptive behavior of three groups of perinatally androgenized females was indistinguishable from that of both male and female controls. However, after gonadectomy and administration of TP, control males and females that had received TP prenatally plus on Day 3 were significantly more receptive than were control females. The induction of receptivity by TP was significantly inhibited by simultaneous administration of the antiestrogen MER-25.