c-Abl is a cytoplasmic tyrosine kinase involved in several signal transduction pathways. Here we report that c-Abl is involved also in insulin receptor signaling. Indeed, c-Abl tyrosine kinase is activated upon insulin stimulation. Inhibition of c-Abl tyrosine kinase by STI571 attenuates the effect of insulin on Akt/GSK-3ß phosphorylation and glycogen synthesis and, at the same time, it enhances the effect of insulin on ERK activation, cell proliferation and migration. This effect of STI571 is specific of c-Abl inhibition, because it does not occur in abl-null cells and is restored in c-Abl-reconstituted cells. Numerous evidences suggest that Focal Adhesion Kinase (FAK) is involved in mediating this c-Abl effect. First, anti-phosphotyrosine blots indicate that c-Abl tyrosine kinase activation is concomitant with FAK dephosphorylation in response to insulin, whereas c-Abl inhibition is accompanied by FAK phosphorylation in response to insulin, a response similar to that observed with IGF-I. Second, the c-Abl effects on insulin signaling are not observed in cells devoid of Focal Adhesion Kinase (FAK -/- cells). Taken together these results suggest that c-Abl activation by insulin, via a modification of FAK response, may play an important role in directing mitogenic versus metabolic IR signaling.