Localization of mercury compounds was investigated in selective regions of the male reproductive tract using autometallography. The results demonstrated that mercury was observed in Sertoli and Leydig cells in testis, but not in the epithelial cells of rete testis and germ cells. In the efferent ductule, mercury compounds were observed in the cytoplasmic compartments of epithelial cells in the proximal and common regions, while they were observed in the supranuclear cytoplasmic compartments in the conus region. In the epididymis, the compounds were observed in the cytoplasmic compariments of narrow and basal cells, but not in the principal cells of the initial segment. In contrast, the compounds were evenly detected in the cytoplasmic compartments of principal cells in the caput. In the corpus and caudal epididymis, the compounds were observed in the basal region of principal cells. The data shows that mercury is differentially accumulated in the male reproductive tract in a region-specific manner.