Pretreatment of rats for 4 days with the selective dopamine D, receptor agonist A-77636 attenuated the ability of cocaine to induce locomotor hyperactivity and to stimulate the expression of the proto-oncogene c-fos in the striatum and nucleus accumbens. Our results suggest that repeated D-1 agonist treatment leads to subsensitivity of D-1 receptors involved in mediating some of the effects of cocaine on behavior and gene expression.