In view of similarities between the behavioral, biochemical, and electrophysiological effects of amphetamine and stress, we tested the hypothesis that presentation of a stressor, mild tail pressure, can sensitize an animal to the later effects of amphetamine, and vice versa. Our findings supported this hypothesis and suggest that amphetamine and at least some stressors may be interchangeable in their ability to induce a sensitization. The data raise the possibility that stress might be a common variable contributing to both amphetamine psychosis and some forms of schizophrenia.