Myofibroblast differentiation and activation by transforming growth factor-β1 (TGF-β1) is a critical event in the pathogenesis of human fibrotic diseases, but regulatory mechanisms for this effect are unclear. In this report, we demonstrate that stable expression of the myofibroblast phenotype requires both TGF-β1 and adhesion-dependent signals. TGF-β1-induced myofibroblast differentiation of lung fibroblasts is blocked in non-adherent cells despite the preservation of TGF-β receptor(s)-mediated signaling of Smad2 phosphorylation. TGF-β1 induces tyrosine phosphorylation of focal adhesion kinase (FAK) including that of its autophosphorylation site, Tyr-397, an effect that is dependent on cell adhesion and is delayed relative to early Smad signaling. Pharmacologic inhibition of FAK or expression of kinase-deficient FAK, mutated by substituting Tyr-397 with Phe, inhibit TGF-β1-induced α-smooth muscle actin expression, stress fiber formation, and cellular hypertrophy. Basal expression of α-smooth muscle actin is elevated in cells grown on fibronectin-coated dishes but is decreased on laminin and poly-D-lysine, a nonintegrin binding polypeptide. TGF-β1 up-regulates expression of integrins and fibronectin, an effect that is associated with autophosphorylation/activation of FAK. Thus, a safer and more effective therapeutic strategy for fibrotic diseases characterized by persistent myofibroblast activation may be to target this integrin/FAK pathway while not interfering with tumor-suppressive functions of TGF-β1/Smad signaling.