A combined technique of autoradiography and immunohistochemistry is described for localization of radioactively labeled ligands and antibodies to neuropeptides, protein hormones and neurotransmitter synthesizing enzymes in the brain. This method permits the simultaneous visualization of radioactively labeled cells and neuropeptide-producing cells in the same tissue preparation. Autoradiograms are fixed with weak paraformaldehyde solution prior to photographic processing for subsequent immunoperoxidase staining. With this procedure 3H-estradiol is localized in neurophysin I and arginine vasopressin-producing cells of the mouse supraoptic and paraventricular nuclei, neurophysin-producing cells of the guinea pig hypothalamus, and dopamine-β-hydroxylase-containing neurons of the rat lower brainstem; 3H-dihydrotestosterone in pituitary gonadotropes and thyrotropes; and 3H-1,25-(OH)2 vitamin D3 in pituitary thyrotropes and pancreatic B-cells.