Antigen-induced cross-linking of immunoglobulin E (IgE) antibodies bound to the high-affinity IgE receptor (FcepsilonRI), on mast cells results in the release of mediators that initiate an inflammatory response. This normal immune response has been abducted by immunological adaptation, through the production of IgE antibodies to normally innocuous substances, to cause allergic disease. Therefore, understanding the molecular requirements in IgE-dependent mast-cell activation holds promise for therapeutic intervention in disease. Recent investigation on the functional coupling of FcepsilonRI to the intracellular signaling apparatus has provided paradigm-altering insights on the importance and function of Src family protein tyrosine kinases (Src PTK) in mast-cell activation. In this synopsis, we review the current knowledge on the role of the Src PTKs, Fyn and Lyn, in mast-cell activation and discuss the implications of our findings on allergic disease.