The distribution of cells capable of concentrating androgen was studied in the male hamster after injection of 5 alpha-dihydro-[1,2,4,5,6,7,(n)-3H]testosterone([3H]DHT) using the technique of thaw-mount autoradiography. Castrated adult male hamsters were injected with 0.2 microgram/100 g body weight of [3H]DHT (107 Ci/mmol) and killed 1.5 h later. Brains were rapidly removed and processed for autoradiography. Localization of radioactivity in high concentrations occurred chiefly in limbic forebrain structures and hypothalamic nuclei associated with the control of reproductive function including the following areas: the septal-preoptic region, the amygdala, and the anterior, ventromedial and arcuate nuclei of the hypothalamus. In addition, labeled cells in lesser concentrations were found in the lateral preoptic area, lateral hypothalamus, hippocampus, mesencephalon and various cortical regions. Treatment with 100-fold excess of testosterone, but not estradiol or diethylstilbestrol, inhibited nuclear localization. These studies provide information on the precise anatomical localization of androgen concentrating cells in the hamster brain and demonstrate the similarity of distribution of androgen binding in the rat, mouse and hamster.