Female hamsters exposed to androgen during the critical period of sexual differentiation have masculinized external genitalia and may exhibit behavioral defeminization and masculinization. There is some controversy as to whether the critical period of the hamster is limited to the postnatal (neonatal) period or includes the prenatal period as well. To date, studies have focused on the behavioral effects of perinatal hormones but have neglected to examine whether perinatal androgen treatment affects the stimulus value of these animals. I propose to study the sexual attractivity (i.e. the female's stimulus value in evoking sexual responses by male conspecifics) of both prenatally and postnatally androgenized female hamsters to sexually experienced male conspecifics. This will be accomplished by observing male hamsters in a series of paired preference tests in which they are given a choice of: 1) prenatally androgenized female vs. postnatally (neonatally) oil-injected control female; and 3) prenatally androgenized female vs. post-natally (neonatally) androgenized female. The stimulus females presented in the preference tests will be anesthetized so that behavioral cues are unavailable to the test males. In this manner, all proceptive and receptive behaviors of the female will be eliminated, thereby ensuring that sexual attractivity is the only factor differing among painrs of stimulus animals. The amount of time males spend investigating various anatomical areas of the stimulus females as well as the occurrence of sexual behavior (e.g. mounts) will be recorded. Should the results of initial tests in which the stimulus animals are anesthetized prove to be significant, males will be given olfactory preference tests in an olfactometer. In examining the effects of perinatal hormones on female attractivity, these studies will extend our understanding of changes which occur during the critical period of sexual differentiation in mamals.