We have reported that sexual behavior of male rats is impaired by long-term psychological stress. We measured dopamine (DA) and its metabolites (3,4-dihydroxyphenylacetic acid, DOPAC, and homovanillic acid, HVA) in the brain of rats which were exposed to the long-term stress. Our experiment was focused on the medial preoptic area (MPOA), which is perhaps the single most critical area of the brain mediating sexual behavior, the amygdala, the substantia nigra, the striatum, the nucleus accumbens and the cortex. In the MPOA, dopamine, DOPAC, and HVA decreased; in the substantia nigra and amygdala, dopamine and HVA decreased; and in the striatum and nucleus accumbens only HVA decreased after long-term psychological stress. In the cortex, however, no evidence of change was recognized. These changes indicate low activity of dopamine neurons which have an important role in male sexual behavior. Therefore, we suspect that exposure of male rats to psychological stress leads to a decrease in the activity of dopamine neurons, especially in the MPOA, amygdala, and substantia nigra, impairing their sexual behavior.