Agonistic, locomotor, and stereotyped behavior were measured in male Swiss-Webster mice in their home cage, normally shared with a female, while confronting an intruder mouse. Acute administration of d-amphetamine (2, 4, 8 mg/kg, IP) to resident mice decreased the frequency of attacks toward an untreated intruder, increased the resident's locomotor activity, and induced a small amount of stereotyped behavior. Redetermination of dose-effect functions during chronic treatment (8 or 16 mg/kg/day) indicated that tolerance did not develop to the antiaggressive effect of d-amphetamine. By contrast, the chronically treated mice showed sensitization to amphetamine-induced stereotypies and a diminished sensitivity to the drug's enhancement of locomotor activity. Subsequent tests with cocaine indicated no differences between amphetamine-maintained and saline control animals, providing no evidence for cross-tolerance or cross-sensitization between cocaine's and amphetamine's effects on attack, locomotion, and stereotypies.