The implanted cylinder model was used to measure LDH activity and lactate and pyruvate concentrations in the extracellular fluid of wounds and wound tissue. Total LDH activity corresponded directly to lactic acid concentration and inversely to oxygen availability. LDH isoenzymes in wound fluid were in an anaerobic pattern soon after injury and evolved toward the aerotic pattern as oxygen supply more nearly matched metabolic capacity. Lactate levels in the wound space are elevated soon after wounding and remain elevated far above those in blood. These data again indicate that wound metabolism is characterized by a relatively poor oxygen supply. Current data from several sources indicate that lactate found in the hypoxic area of the wound may stimulate collagen synthesis in fibroblasts lying in the high lactate environment. We postulate that elevated concentration of lactate in wounds is a major signal for collagen synthesis and repair.