Mast cells and/or basophils have been implicated in the expression of a wide variety of biological responses, including immediate hypersensitivity reactions, host responses to parasites and neoplasms, angiogenesis, tissue remodeling, and immunologically non-specific inflammatory and fibrotic conditions. Recent findings suggest that an important mechanism by which mast cells influence such biological responses is through the production of a broad panel of multifunctional cytokines. In contrast, the extent to which basophils can produce cytokines is uncertain.