Abstract
Ss were 6 male and 6 female children with Down's syndrome (mongolism) who interacted in dyads in sexually homogeneous and heterogeneous free-play situations. Actual, observable behaviors were recorded to investigate sex differences in, and the influence of sex of peer on, social and play behavior. Girls engaged in more sedentary activities than boys and sexual homogeneity resulted in less sedentary activity than sexual heterogeneity. Peer-sex seems to influence more the type rather than the amount of social interaction with male mongoloids being more influenced by peer-sex than girls. Implications of the results for future studies of mental retardate social behavior and studies of the stereotypic conception of mongoloids as cheerful, friendly, and so forth, were discussed.