Vascular smooth muscle cell (VSMC) apoptosis has been demonstrated in vascular lesions, such as atherosclerotic and postangioplasty restenotic lesions. Balloon injury also induces VSMC apoptosis. Fas is a death factor that mediates apoptosis when it is activated by its ligand, FasL. Fas-mediated apoptosis was found to be implicated in the pathogenesis of vascular diseases in which Fas/FasL expression was detected. We investigated whether the Fas/FasL interaction mediated acute and chronic VSMC apoptosis and lesion formation in a vascular injury model that may resemble balloon angioplasty. A large spring wire was inserted into the femoral artery of C3H/HeJ (wild-type), C3H-gld (Fas ligand-/-), and C3H-lpr (Fas-/-) mice. The wire was left in place for 1 minute to denude and expand the artery. Massive apoptosis was observed in medial VSMCs from 1 to 7 hours later. There was no difference in the number of apoptotic cells among the 3 groups of mice 4 hours after injury. At 4 weeks, the injured arteries presented signs of concentric neointimal hyperplasia composed exclusively of VSMCs. There was no difference in the degree of neointima hyperplasia (intima/media ratios were as follows: wild type 1.4+/-0.3, gld 1.0+/-0.2, and lpr 1.3+/-0.2) or in the number of apoptotic nuclei among the 3 groups. These findings suggest the existence of other signaling pathways for acute and chronic VSMC apoptosis, at least that induced by mechanical vascular injury.