Human mast cells and basophils participate in allergic inflammation by releasing preformed and newly synthesized mediators upon cross-linking of cell surface IgE/receptor complexes with specific antigen. It is becoming increasingly apparent, however, that the basophil response is up-regulated by a far greater number of cytokines than is the mast cell, making the basophil more sensitive to products that are commonly generated during immune reactions. As a result, basophils may have a greater role in the chronic allergic inflammation that characterizes diseases such as asthma. This belief is supported further by the fact that the basophil has recently been shown to generate interleukin-4, and possibly other cytokines, indicating a role for this cell in directing the immune response of other cell participating in allergic lesions.