AbstractA murine monoclonal antibody (NaM19–3C4, IgG1, Kappa) was produced from splenocytes of mice immunized with red blood cells. The antibody agglutinated untreated Ge:2,3,4 and Ge:‐2,3,4 erythrocytes in indirect antiglobulin test but failed to agglutinate trypsin‐treated cells. Gerbich‐negative erythrocyte of the Leach‐ (Ge:‐2,‐3,‐4) and of the Gerbich‐ (Ge:‐2,‐3,4) types were not recognized by the antibody. Immunoblotting experiments showed that the antibody bound to glycophorins C and D from control erythrocytes and to the abnormal glycophorin C identified in the Gerbich‐negative cells of the Yussef type (Ge:‐2,3,4). No binding to the altered glycophorin C from Ge:‐2,‐3,4 erythrocytes was observed, indicating that the antibody specifically recognized the Ge:3 epitope localized within re