Play behaviours are exhibited by many mammalian species. The similarity of such behaviour across children, non-human primates and rats makes it an especially appropriate target for the investigation of drug- or toxicant-induced disruption. In this study the acute effects of cocaine on play behaviour in male and female Sprague-Dawley rats was assessed. Same-sex dyads of rats (postnatal day 35-36) were separated 24 h prior to testing. On the following day, one or both rats of the dyad were injected with the same dose of cocaine (0, 2.5, 5.0 or 20.00 mg/kg). Thirty minutes later the rats were placed together and, after 5 min of habituation, the frequency of pins and crawl-overs were measured for each subject. In dyads in which both rats were treated, crawl-overs and pinning behaviour were decreased by 20 mg/kg cocaine. In dyads in which only one rat was treated, there was marginal effect of cocaine treatment on pinning frequency, while crawl-overs were unaffected. Pinning frequency was not sexually dimorphic in either type of dyad; however, crawl-overs were more frequently exhibited by females in dyads in which only one rat was treated. Thus, pinning behaviour in juvenile rats appears somewhat more sensitive to cocaine-induced disruption than crawl-over behaviours. Additionally, the presence of an untreated rat appears to attenuate the play-disrupting effects of cocaine on pinning frequency.