Androgen-receptor upregulation that occurs with androgenic-anabolic steroid (AAS) administration may be mediated by AAS metabolites, dihydrotestosterone (DHT), and estrogen. Castrated and intact male rats received 14 s.c. daily injections of AAS (2 mg/kg testosterone cypionate, 2 mg/kg nandrolone decanoate, and 1 mg/kg boldenone undecylenate in sesame oil vehicle), DHT (5 mg/kg dihydrotestosterone), EB (5 mg/kg estradiol benzoate), or sesame oil vehicle. Approximately 18-24 h after the fourteenth injection, brain tissues were removed and processed immunocytochemically using the PG-21 androgen-receptor antibody. As reported before, castration eliminated AR-ir (androgen-receptor immunoreactivity) and AAS upregulated AR-ir in the ventromedial hypothalamus (VMHVL), medial amygdala (MePV), and medial preoptic area (MPOM). When compared to AAS, DHT fully upregulated AR-ir in the VM VL and MPOM and partially upregulated AR-ir in the MePV. EB treatment partially upregulated AR-ir in the VMHVL and MePV, but not in the MPOM of castrated rats. Because AR-ir in the MPOM was consistently upregulated by DHT or AAS, and not EB, androgen-receptor availability in this region may be mediated specifically via androgen receptors.