Treatment with d-amphetamine has been shown to cause a decrease in play fighting by juvenile rats. Previous studies, however, did not determine if all behavioral components of play were equally diminished. In this study, the effects of amphetamine on both the attack and defense patterns of play fighting were analyzed. Experiment 1 shows that a 0.5 mg/kg dose, injected subcutaneously in the nape, decreases both attack and defense. In contrast, Experiment 2 shows that the same dose, injected subcutaneously in the hip, decreases the level of attack to a similar level, but does not significantly affect defense. This suggests that while the 0.5 mg/kg dose of amphetamine is primarily affecting the attack components of play, via its action on the central nervous systems, the reduced likelihood of defense for those rats injected in the nape probably results from a local anesthetic effect, which numbs the area of the body defended during play fighting. Further doses (0.15 & 1.0 mg/kg), injected in the hip, were also tested. The highest dose decreased both components of play. The lowest dose had no effect on either attack or defense. It is suggested that the attack and defensive components of play fighting may be mediated by different neural systems.