Male and female juvenile rats were individually exposed to nonplayful juvenile social stimuli in a novel test of play-soliciting behavior to examine hormonal and experiential determinants of sex differences. In Experiment 1, neonatally androgenized females engaged in play soliciting at a level equal to that of male controls and greater than that of nonandrogenized female controls. In Experiment 2, males and females were reared in unisexual and bisexual groups in order to compare long-term sex-related social experience effects on juvenile play soliciting. Males exposed only to other young males engaged in greater play soliciting than males exposed to both sexes; females, in contrast, were unaffected by sex of cagemates. Within rearing conditions, however, males engaged in greater play soliciting than females. The combined results suggest that perinatal gonadal androgen exposure effects on social play are prepotent and contribute essentially to sex differences in the initiation of social play behavior.