Doublesex- and mab-3-related transcription factor 1 (DMRT1) is a transcription factor that plays a key role in male sex determination and differentiation by controlling testis development and male germ cell proliferation. DMRT1 plays a central role in spermatogonia by inhibiting meiosis in undifferentiated spermatogonia and promoting mitosis. DMRT1 is specifically expressed in spermatogonia and spermatocytes in normal tissues. Amplification of DMRT1 is associated with spermatocytic seminomas. Antibody to DMRT1 may be useful for identification of spermatocytic seminoma.