The effects of radical neonatal decortication on the social play of juvenile rats, as well as the effects of neonatal ablation of frontal or parietal cortex, were examined in this series of experiments. When total decorticates were tested in like-lesioned pairs, the frequency of pinning was reduced by about 50% and their average pin durations were shorter. Nevertheless, the play of decorticates appeared essentially normal in general appearance, and did not differ from controls in a measure of overall play vigor using an electronic activity platform. Further, there were no differences in pin frequencies when controls and decorticates were paired together in cross-lesion testing. Separate tests of play solicitation behaviors did not detect any differences between controls and decorticates suggesting that play motivation was essentially intact after decortication. No deficits in pinning resulted from frontal ablations; however, pin durations were shorter in like-lesion testing. In cross-lesion testing, there was an increase in dorsal contacts and a trend toward shortening of pin durations. Parietal aspirations resulted in a 65% reduction in pin frequency, without substantially altering dorsal contacts. Anesthetization of the anterior surface of the animal's back with xylocaine reduced pinning in controls but eliminated pinning in parietals. Although the results generally indicate little participation of the neocortex in the instigation of rough-and-tumble play, the reliable numerical changes that were observed may be explained by apparent motor changes as well as reduced somatosensory sensitivity.