Abstract. Male-specific transplantation antigen H-Y was proposed to be the testis-determining factor (TDF) in 1975, while SRY was found to be the TDF gene in 1990. What then of H-Y antigen? H-Y antigen was categorized into two entities, viz., T-cell mediated H-Y antigens (H-Y) and serologically detectable male antigens (SDM). Several HY genes such as Smcy, Uty and Dty have been identified and these are all Y-Iinked. H-Y is male-specific and clinically important in cell, tissue, or organ transplantations. Male-enhanced antigen 1 (Meal) was isolated from an expression library using polyclonal anti-H-Y antibody. We cloned and characterized mouse and bovine Meal/MEAI, the gene product of which was mainly localized in elongated spermatids. Mea2 was identified using monoclonal anti-H-Y antibody. MEA2 protein is localized in the Golgi apparatus of spermatocytes and spermatids. Colocalization of MEA2 protein with y-adaptin in clathrin-coated vesicles was demonstrated. Disruption of Mea2 resulted in spermatogenic failure. These findings suggest that Mea2 is involved in transportation of materials needed for acrosome components in spermatogenesis. Its human homologue is Golgin-160 which was detected in an SLE autoimmune disease patient. Müllerian inhibiting substance (MIS) was reported to have SDM activity. Taken together, SDM is a collective name for protein antigens associated with testis activity (MIS) or spermatogenesis (MEA1, MEA2) and may be antigenic when expressed in females. From the viewpoint of autoimmune diseases, the Identification and characterization of SDMs will be clinically important.