We recently demonstrated that immunoglobulin E (IgE), in the absence of cross-linking agents, activates signaling pathways in healthy murine bone marrow-derived mast cells (BMMCs) and that this activation enhances BMMC survival, at least in part, via secretion of autocrine-acting cytokines. We report herein that IgE alone also triggers the adhesion of both BMMCs and connective tissue mast cells (CTMCs) to the connective tissue component, fibronectin (FN). This adhesion occurs to the same extent as that triggered by optimal levels of Steel factor (SF) or IgE + antigen (IgE + Ag) and is mediated by an increased avidity of the integrin very late antigen 5 (VLA-5). Moreover, this IgE-induced adhesion, which is prolonged compared with that elicited by SF or IgE + Ag, requires phosphatidylinositol 3-kinase (PI3K), phospholipase C gamma (PLCgamma), and extracellular calcium but not extracellular-regulated kinase (Erk) or p38. Interestingly, we found, using the calcium channel blocker, 2-APB (2-aminoethoxydiphenyl borate) and Lyn-/- BMMCs that both IgE- and IgE + Ag-induced adhesion to FN require extracellular calcium entry, whereas SF does not. Furthermore, our data suggest that FN acts synergistically with IgE to prolong intracellular phosphorylation events and to enhance IgE-induced inflammatory cytokine production and BMMC survival.