Abstract. Platelet-derived growth factor (PDGF) and transforming growth factor-~ (TGF-/~) markedly potentiate tissue repair in vivo. In the present experiments, both in vitro and in vivo responses to PDGF and TGF-B were tested to identify mechanisms whereby these growth factors might each enhance the woundhealing response. Recombinant human PDGF B-chain homodimers (PDGF-BB) and TGF-B1 had identical dose-response curves in chemotactic assays with monocytes and fibroblasts as the natural proteins from platelets. Single applications of PDGF-BB (2 #g, 80 pmol) and TGF-B1 (20 #g, 600 pmol) were next applied to linear incisions in rats and each enhanced the strength required to disrupt the wounds at 5 d up to 212% of paired control wounds. Histological analysis of treated wounds demonstrated an in vivo chemotactic response of macrophages and fibroblasts to both PDGF-BB and to TGF-/~ 1 but the response to TGF-B1 was significantly less than that observed with PDGF-

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