Enhanced wound healing is elicited by exogenous administration of transforming growth factor- beta 1 (TGF- beta 1) in split-thickness, excisional wounds in the pig (Quaglino, Lab Invest 63:307-319, 1990). A study was designed to investigate if the selective and localized effects of TGF-beta 1 found in the previous model were dependent upon the type of wound or could be considered a more general effect of the cytokine. Transdermal, sutured incisions in the pig were evaluated by conventional histology and by in situ hybridization to reveal locally affected gene expression of collagen, elastin, fibronectin, stromelysin, TGF- beta 1, and basic fibroblast growth factor. Granulation tissue formation was markedly enhanced at 6 d by a single injection of recombinant human TGF beta 1 at the time of wound closure. Although granulation tissue was confined within the margins of the incisional wound, prominent differences in hybridization signals were observed between control and treated wounds. The stimulatory effect of TGF- beta 1 on granulation tissue formation was accompanied by a distinct enhancement in cells expressing mRNA for several different extracellular matrix proteins including collagens type I and III and elastin, whereas a single injection of human recombinant TGF beta 1 (4 micrograms) at the wound site diminished the expression of the neutral metalloprotease, stromelysin, and enhanced the frequency and intensity of cells expressing TGF- beta 1. The data reinforce the concept that TGF- beta 1 can act as a potent, auto-inductive modulator of connective tissue remodeling during the repair process.