['The presence of multiple blood clots in leucocyte-depleted erythrocyte concentrates during a transfusion gave rise to an investigation to find the exact cause.', 'Determination of the various blood group systems was carried out using the gel centrifugation method and also the polymerase chain reaction (PCR) using sequence-specific primers. In addition the human leucocyte antigens (HLA) class 1 and class 2 markers were determined with molecular biological methods.', 'The erythrocytes in the blood bags containing the blood clots showed a mixed-field agglutination in each blood group where the donor and recipient had different phenotypes. The HLA groups, however, could be solely attributed to the patient, since during the preparation of erythrocyte concentrates all leucocytes are removed and only very few residual cells containing DNA are present.'] Does [ Blood clots in erythrocyte concentrate during transfusion ]?