Target neurons for 3H-corticosterone were identified by autoradiography and tyrosine hydroxylase containing neurons were identified by immunocytochemistry in the same sections of lower brain stem of 38-day-old rats, 10-day-old rats and adult mice. In all animals studied, the same topographic distribution of neurons was found which exibited a nuclear accumulation of 3H-corticosterone. Target neurons for 3H-corticosterone were widely distributed in the brain stem. Motor neurons of the cranial nerves and certain neurons of the reticular formation were among the most heavily labeled cells. Neurons containing immunoreactive tyrosine hydroxylase were detected in all of the classical noradrenergic and adrenergic cell groups. Tyrosine hydroxylase containing neurons did not concentrate radioactivity, but were found in close proximity to neurons which concentrated the radiolabeled glucocorticosteroid, especially in the ventrolateral medulla (area Ai) and in the ventrolateral pons (area A5). These results do not support, but do not exclude, a direct genomic action of corticosterone on catecholamine neurons in the lower brain stem.