Two experiments were performed with adult male rats of the Long-Evans strain to determine the specificity of fluprazine hydrochloride in decreasing offensive attack. Both 4 and 8 mg/kg doses (IP) significantly reduced offense by resident males selected for high or medium levels of aggression when tested with intruders 30 min postinjection. No reliable differences in other social or nonsocial behaviors were observed. Drug treatment resulted in an overall reduction in offensive behavior of more than 70% in both groups. Actual biting and wounding of intruders by treated subjects was decreased by as much as 98%. A second experiment assessed the drug's influence on defense in the "shock-elicited aggression" paradigm. While duration of boxing to multiple intermittent shocks was significantly suppressed by drug administration (4 and 8 mg/kg), the same doses had no effect on postshock duration of boxing, or sonic and ultrasonic vocalizations following several high intensity (1.5 mA) shocks. These findings are consistent with other research on this and related phenylpiperazine compounds, indicating that its action is specific in reducing offense with minimal influence on social or defensive behavior.