HLA antigens on erythrocytes were assessed concurrently by three tests--the indirect antiglobulin, two-stage bromelin and absorption test--using polyspecific and monospecific sera against HLA antigens A1, A2, B7, B8 and B12. Evidence obtained by the bromelin test was successful only in rare instances. The positivity of the absorption test increased with the number of saturations: after triple saturation of the HLA serum with erythrocytes of the same subject readings were obtained twice to three times more frequently than after single absorption. As compared with the indirect antiglobulin test, the positive erythrocyte reactions in the absorption test were less frequent: with polyspecific HLA sera in 36.97% as compared with 78.15%, with monospecific HLA sera in 63.64% as compared with 100%. The absorption test is a suitable method for detection of HLA antigens on erythrocytes, supplementing the indirect antiglobulin test.