The likelihood of male-to-female physical aggression on days of male partners' substance use, during a 15-month period, was examined. Participants were from married or cohabiting partner violent men entering a drug abuse treatment program (N=149). Compared to days of no drug or alcohol use, the likelihood of male-to-female physical aggression was significantly higher on days of substance use, after controlling for male partners' antisocial personality (ASP) disorder and couples' global relationship distress. Of the psychoactive substances examined, the use of alcohol and cocaine was associated with significant increases in the daily likelihood of male-to-female physical aggression; cannabis and opiates were not significantly associated with an increased likelihood of male partner violence.