Severity of fibrosis after injury is determined by the nature of the injury and host genetic susceptibility. Metabolism of collagen, the major component of fibrotic lesions, is, in part, regulated by integrins. Using a model of glomerular injury by adriamycin, which induces reactive oxygen species (ROS) production, we demonstrated that integrin α1-null mice develop more severe glomerulosclerosis than wild-type mice. Moreover, primary α1-null mesangial cells produce more ROS both at baseline and after adriamycin treatment. Increased ROS synthesis leads to decreased cell proliferation and increased glomerular collagen IV accumulation that is reversed by antioxidants both in vivo and in vitro. Thus, we have identified integrin α1β1 as a modulator of glomerulosclerosis. In addition, we showed a novel pathway where integrin α1β1 modulates ROS production, which in turn controls collagen turnover and ultimately fibrosis. Because integrin α1β1 is expressed in many cell types this may represent a generalized mechanism of controlling matrix accumulation, which has implications for numerous diseases characterized by fibrosis.