Metal responsive transcription factor-1 (MTF-1) is ubiquitously expressed in various tissues, and is thought to be an intracellular zinc sensor that regulates transcriptional activation of zinc responsive genes. We investigated the distribution of MTF-1 in the mouse testis, where zinc plays an essential role in spermatogenesis. By performing immunohistochemical analysis of the ddY mouse testis using the anti-MTF-1 antibody, we observed a donut-shaped staining pattern in the seminiferous tubules in the region proximal to the lumen, where spermatocytes primarily localize. A similar staining pattern was obtained using in situ hybridization to detect MTF-1 mRNA. Furthermore, we confirmed that MTF-1 could not be detected at both the protein and mRNA levels in the premature 20-d-old mouse testis, where spermatocytes are thought not to have been formed in the seminiferous tubules yet. These lines of evidence strongly indicated the selective expression of MTF-1 in mouse spermatocytes and suggested that MTF-1 played a role in a certain stage of spermatogenesis.