This study compares the subtypes of central beta adrenergic receptors (ARs) of brains of untreated rats with those of imipramine-treated rats. Beta adrenergic receptors were measured by quantitative autoradiography of the binding of 3H-dihydroalprenolol (3H-DHA) in coronal sections of rat brain. Repeated treatment of rats with imipramine significantly reduced the binding of 3H-DHA to beta-1 AR in many brain areas, especially throughout the cerebral cortex, hippocampus, thalamus, and amygdala. Significant reductions of the binding of 3H-DHA to beta-2 AR were not found in any area of the brain. These data suggests that a selective down-regulation of beta-1 AR may be involved in the adaptive changes occurring after prolonged imipramine treatment.