A genetic antigen, Gm(n), has been described for the Ne subgroup of gamma-globulin previously devoid of Gm factors. It was detected by precipitin tests with a primate antiserum to Ne-type heavy chains. A relation to the Gm(b) antigens of the Vi subgroup and the Gm(f) and Gm(y) antigens of the We subgroup was apparent. The availablity of genetic antigens for the heavy chains of three subgroups of gamma-globulin with varying relationships in different populations offers an approach to the mapping of the genes concerned.