Investigated rough and tumble play (RTP), a prosocial behavior whose expression and purpose varies as a function of gender, in 43 preschoolers, part of a longitudinal sample (targets), and 86 playmates (partners). A "playroom on wheels" was designed to maximize the amount of RTP displayed in same-sex triads. Observational coding techniques were devised to record various active and verbal behaviors, including a measure of activity level. Results indicate both quantitative and qualitative differences in the behaviors of the male and female triadic groups. Further, a robust sex difference in the amount and intensity of RTP was observed for both targets and partners. Analyses of the behavioral components indicated that RTP was distinct from other dominance-oriented or aggressive behaviors in this age group. A hypothesis concerning differential salience of interpersonal cues is presented to account for these findings, and speculations are made concerning the influence of RTP on subsequent development. (18 ref) (PsycINFO Database Record (c) 2012 APA, all rights reserved)