DL-amphetamine's actions on brain polyribosomes were studied in crowded and uncrowded mice. The administration of 20 mg/kg DL-amphetamine induced disaggregation of brain polyribosomes in both crowded and uncrowded mice 30 min post drug administration. However, the magnitude of polysome dissociation was observed to be greater in crowded animals than in uncrowded ones. In studying the dose-response relationship there appears to be a relationship between drug dose and polysome disaggregation in both groups of animals, although the effects were always greater in crowded mice. The magnitude of polysome dissociation appears to parallel both in the intensity of central nervous system stimulation, and degree of crowding. Haloperidol was able to block the increased locomotor activity due to drug dose and crowding at 1 mg/kg, and significatnly suppress disaggregation of brain polysomes in crowded animals. A possible role of the effects of crowding on the central nervous system in the presence of amphetamine as it relates to polysome dissociation has been presented.