The purpose of the present experiments was to investigate conditions under which alcohol and chlordiazepoxide (CDP) enhance aggression. Alcohol (300, 600, and 1200 mg/kg orally) and CDP (5, 10, and 20 mg/kg) failed to alter attack behavior in male mice confronting intruder mice in their home cages. When confrontations between attack-experienced mice and group-housed mice occurred in a neutral cage, attack and threat behavior was suppressed to about 50% of that in the resident's home cage. A low dose of alcohol (300 mg/kg) more than doubled the frequency of attacks and threats in the neutral cage. Higher doses of both drugs decreased attacks in the neutral cage. Combined administration of low doses of alcohol (150 and 300 mg/kg) and CDP (2.5 and 5.0 mg/kg) increased attack and threat frequency in the neutral cage to a larger extent than when either drug was given itself. The aggression-enhancing effects of alcohol and CDP in the neutral cage situation are consistent with the view that both drugs can lead to behavioral disinhibition. Alternatively, the results could reflect simply the ratedependency of alcohol effects on attack behavior, that is, low rates are increased whereas high rates remain unaffected. The present results also provide evidence for an additive interaction of both drugs in their depressant effects and, also, in their aggressionheightening effects.