Six monoclonal antibodies (KOR-E1-E6) were raised against human erythrocyte membrane antigens. Aggregating reactions of normal human erythrocytes with or without enzyme treatment and specific antigen deficient (null type) erythrocytes were used for detection of the antigens. SDS-polyacrylamide gel electrophoresis with Western blotting and immunoperoxidase methods were also used to confirm the results. The antigen recognized by KOR-E1 and KOR-E5, which was sensitive to protease, trypsin, and neuraminidase, and only expressed on human erythrocytes, was identified as Pr1h. The antigen recognized by KOR-E2 and KOR-E6 was identified as the EnaTS portion of glycophorin A, because the antigen was sensitive to protease and trypsin, but resistant to neuraminidase, and was not present on En(a-) erythrocytes. The antigen recognized by KOR-E3 that was protease-, trypsin-, and neuraminidase resistant, and absent on En (a-) erythrocytes, was identified as Wrb antigen. As KOR-E4 reacted with all erythrocytes examined, the antigen it recognizes could not be determined.