Summary. To detect human granulocyte-reactive antibodies, a glycoprotein-specific enzyme immunoassay for platelet antibodies was adapted for the use of granulocytes as target cells. Peripheral blood granulocytes were simultaneously incubated with a monoclonal antibody (mAb) and the serum to be investigated. After solubilization, aliquots of the cell lysate were transferred to plastic tubes coated with goat anti-mouse antibodies. Following immobilization of the trimolecular (mAb-glycoprotein-human antibody) complex it was detected by addition of enzyme-labelled goat anti-human antibodies using a luminescence technique. This assay allowed identification of different granulocyte-reactive antibodies present in the same sample without the need for complicated absorption studies. Alloantibodies against HLA and the granulocyte-specific NA antigens as well as isoantibodies against the Fc-gamma-receptor III (FcRIII) were detectable using mAb-specific immobilization of granulocyte antigens (MAIGA). Binding of autoantibodies to the FcRIII and to the CD 11b/CD 18 complex could be shown.