In the present study, we investigated the effect of adrenocorticotropic hormone (ACTH) on the immobilization of rats in the forced swim test after the administration of selegiline, a selective and irreversible monoamine oxidase (MAO)-B inhibitor. Single and repeated administration of selegiline significantly decreased the duration of immobility in normal rats. When selegiline was administered for 15 days, we observed a significant decrease in immobility in rats treated with ACTH for 14 days. The immobility-decreasing effect of selegiline was blocked by nafadotride, a selective dopamine D(3)-receptor antagonist in normal and ACTH-treated rats. Selegiline may be useful in an animal model of depressive conditions resistant to tricyclic antidepressant treatment via the dopamine D(3) receptor.