Three different conditions, psychostimulant-induced behavioral sensitization in rodents, psychostimulant-induced psychoses in human, and chronic schizophrenia show similar longitudinal alternations, progressively enhanced susceptibility to abnormal behaviors, psychotic state, and relapse. Sensitization phenomena to the drugs or endogenous dopamine should be involved in the mechanisms underlying the development of such susceptibility. Recently, an enhanced dopamine release in vivo by amphetamine administration in the striatum has been shown in schizophrenics, which is a replication of that previously proven in the behavioral sensitization in rats. Accordingly, common molecular mechanisms of sensitization phenomena must develop in these three conditions, and are overviewed in this review