Sexually experienced, adult male rats were either castrated, castrated and implanted SC with a Silastic capsule containing testosterone (T), or sham operated. Coital performance of castrates gradually declined such that 4 weeks after surgery no males in this group ejaculated whereas 89% and 100%, respectively, of the rats in the castrated, T-treated and the sham-operated groups displayed ejaculation. Males in all three groups were decapitated 33-34 days post-operatively after 10 min exposure either to the behavioral test chamber, with an estrous female restrained in one corner behind a wire mesh screen, or to a home cage. Brains were quickly removed and the caudate-putamen, nucleus accumbens, septum, and preoptic area/anterior hypothalamus were frozen and saved for later estimation of dopamine (DA) and two neural metabolites of DA, 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA). The concentrations of DA, DOPAC, and HVA, as well as the ratio of DOPAC/DA, did not differ significantly in any of the 4 brain regions assayed among males in the three endocrine groups, regardless of whether they were killed after exposure to an estrous female or a home cage. The results fail to support the hypothesis that T-induced alterations in neurotransmission in nigro-striatal, mesolimbic, or incertohypothalamic DA pathways mediate the activational effect of this steroid on masculine sexual behavior.