Degradative events in remodeling connective tissues are mediated through the actions of one or more members of the matrix metalloproteinase family. Conversely, members of the tissue inhibitors of metalloproteinase (TIMP) family act to attenuate proteolysis. Because collagenase and TIMP are rapidly secreted into the extracellular matrix following their biosynthesis and may not remain near their cell of origin, we undertook an immunohistochemical examination of human burn injuries to establish the distribution of these proteins during acute wound repair. Immunostaining for collagenase and TIMP was markedly increased within the wound bed but not in adjacent regions of histologically normal skin. Immunoreactive collagenase was first noted at the eschar-dermal interface by day 3 after injury and became very prominent in the dermis from day 5 to day 17. By day 5, focal patches of immunoreactive collagenase were found at the epidermal-dermal junctions at the wound margins. Within the wound bed, intense staining for collagenase was noted in the connective tissue surrounding the surviving epithelial appendages and around blood vessels. Immunoreactive TIMP was detected by day 2 both in the dermis and the overlying eschar but rapidly assumed the same interfacial pattern as described for collagenase. Staining for TIMP was only sporadically found at the dermal-epidermal margins and surrounding surviving epithelial appendages. Like collagenase, TIMP was prominently localized about vascular structures. These studies demonstrate that, in acute wounds, immunoreactive collagenase and TIMP are generally increased throughout the area of injury but particularly so at interface zones including eschar-dermis, epidermis-dermis, appendages-dermis, and around vascular structures.