Recent investigation into the mechanisms of wound healing has indicated the interaction of many substances, including several growth factors. The activity of platelet-derived growth factor (PDGF) and transforming growth factor beta (TGF-beta), are best defined. Both factors are secreted primarily from the alpha granules of platelets, but also from activated macrophages and fibroblasts. Investigation implicates the platelet as the initiator of wound healing, secreting PDGF, TGF-beta, and other factors that are chemotactic for monocytes, macrophages, and fibroblasts. Although their mode of action and degree of effect are different, both PDGF and TGF-beta increase the collagen content and early rate of gain of strength in wounds in normal and compromised tissue. In normal tissue, however, there is no long-term effect on wound outcome. The use of exogenous growth factors offers potential for chemical manipulation of the healing wound, particularly in tissues that are compromised, or where healing is abnormal.