This study was undertaken to examine whether cadmium oral exposure modifies biogenic amine concentration at hypothalamic level in adult male rats, and to investigate the possible modulatory effects of melatonin against cadmium-induced changes on these neurotransmitters. For this purpose, rats were exposed to cadmium (25 mg/l of CdCl(2) in the drinking water) with or without melatonin (30 μg/rat/day intraperitoneally) for 30 days. Norepinephrine (NE), dopamine (DA), serotonin (5-HT), 3,4-dihydroxyphenyl acetic acid (DOPAC), and 5-hydroxyindoleacetic acid (5-HIAA) were quantified by high performance liquid chromatography (HPLC). Oral cadmium administration led to decrease of NE, DA, and 5-HT content and DA turnover within the three hypothalamic regions examined, and therefore an inhibition of 5-HT turnover at posterior hypothalamus. Sensitivity to melatonin was specific to the hypothalamic region evaluated. Thus, the anterior hypothalamus was not nearly sensitive to exogenously administered melatonin, whereas the neurohormone decreased the content of these amines in the mediobasal hypothalamus, and melatonin increased it in the posterior hypothalamic region. Melatonin effectively prevented some cadmium-induced alterations on hypothalamic amine concentration. This is the case of DA in the anterior and posterior hypothalamus, and 5-HT metabolism in the posterior hypothalamic region. In conclusion, the obtained results indicate that melatonin treatment may be effective modulating some neurotoxic effects induced by cadmium exposure, and, more to the point, a possible role of this indolamine as a preventive agent for environmental or occupational cadmium contamination.