The FcR for IgA (FcαRI, CD89) is primarily expressed on cytotoxic immune effector cells. By chemically cross-linking F (ab′) fragments of the FcR for IgA (FcαRI)-specific mAb (A77) with tumor Ag-specific mAb (anti-HER2/neu and anti-epidermal growth factor receptor), we have developed bispecific molecules (BSM) that simultaneously bind to respective tumor Ags and FcαRI-expressing effector cells in whole blood. These BSM mediated up to 55% of specific lysis of appropriate tumor Ag-expressing target cells (from a variety of tumors) with purified polymorphonuclear leukocytes, monocytes, or whole blood effector cells without preactivation with exogenous cytokines. To our knowledge, this is the first demonstration of Ab-dependent cell-mediated cytotoxic activity via FcαRI in whole blood. Also, monocyte-derived macrophages mediated phagocytosis of HER2/neu-expressing tumor cells (> 95% tumor cell loss). These BSM-mediated cytotoxic activities were completely inhibited by F (ab′) 2 of A77, demonstrating the specific role of FcαRI as a trigger molecule. Furthermore, the binding of these BSM to monocytes or polymorphonuclear leukocytes in whole blood did not induce modulation of FcαRI in the absence of the target Ag. Therefore, immune effector cells may be “armed” with FcαRI-directed BSM in whole blood. These FcαRI-directed BSM may offer new treatment options for various malignancies and other disease conditions.