Human CD32B (FcgammaRIIB), the low-affinity inhibitory receptor for IgG, is the predominant Fc receptor (FcR) present on B cells. Immunohistochemical and expression studies have identified CD32B expression in a variety of B-cell malignancies, suggesting that CD32B is a potential immunotherapeutic target for B-cell malignancies. A high-affinity monoclonal antibody (mAb 2B6), from a novel panel of anti-human CD32B-specific mAbs, was chimerized (ch2B6) and humanized (hu2B6-3.5). Both ch2B6 and hu2B6-3.5 were capable of directing cytotoxicity by peripheral blood mononuclear cells and monocyte-derived macrophages against B-lymphoma lines in vitro. In a human B-cell lymphoma mouse xenograft model, administration of ch2B6 or hu2B6-3.5 reduced tumor growth rate and improved tumor-free survival. Both the in vitro and in vivo activities of 2B6 required an intact Fc, suggesting an FcR-mediated mechanism of action. These data support the hypothesis that CD32B is a viable target for mAb treatment of B-cell lymphoproliferative disorders.