The role of polypeptide growth factors in the processes of inflammation and repair was investigated by analyzing the influence of transforming growth factor-beta (TGF-beta), applied directly to linear incisions made through rat dorsal skin. A dose-dependent, direct stimulatory effect of a single application of TGF-beta on the breaking strength of healing incisional wounds was demonstrated. An increase in maximum wound strength of 220 percent of control was observed at 5 days; the healing rate was accelerated by approximately 3 days for at least 14 days after production of the wound and application of TGF-beta. These increases in wound strength were accompanied by an increased influx of mononuclear cells and fibroblasts and by marked increases in collagen deposition at the site of application of TGF-beta. TGF-beta is thus a potent pharmacologic agent that can accelerate wound healing in rats.