Mammalian response to injury essentially is that of tissue repair and re-epithelialization. The most important component of repair tissue is collagen, and after injury collagen turnover is greatly increased. Collagen biosynthesis is initiated by nuclear DNA of fibroblasts; the steps in biosynthesis are complex but studies of collagen biosynthesis may eventually have clinical potential. Normally, wound healing lasts for up to 2 years but nutritional and metabolic factors, such as malnutrition, delay healing; hyperalimentation would likely be beneficial under these conditions. Other factors that influence wound healing are the oxygen tension in tissues, the hemodynamic status, and the effects of substances such as cortisone, vitamins A and C, and zinc.