BACKGROUND During wound healing, keratinocytes detach from the basement membrane and migrate to cover the exposed connective tissue. Subsequently, the wound clot is degraded gradually and replaced by the epithelial cells and the granulation tissue. Both of these processes are likely to be affected by matrix-modifying enzymes. Type IV collagenases are members of the matrix metalloproteinase family (MMP), which are known to degrade several matrix components. The aim of this study was to investigate the expression of MMP-2 and MMP-9 (72-kd and 92-kd type IV collagenases, respectively) during early human wound healing. METHODS Experimental wounds were created in human oral mucosa and biopsies were taken 1, 3, and 7 days after wounding. In situ hybridization on paraffin sections was used for the detection of messenger RNAs coding for MMP-2 and MMP-9, and the secretion of MMPs into the oral cavity after wounding was followed by zymography. Regulation of MMP-2 and MMP-9 expression by cytokines was studied using cultured mucosal keratinocytes, gingival fibroblasts, and wound granulation tissue fibroblasts. RESULTS By in situ hybridization, the expression of MMP-2 was localized in the connective tissue fibroblasts and endothelial cells during all phases of wound healing. Mucosal epithelium was practically negative for MMP-2 expression. MMP-9 messenger RNA was found in mucosal epithelium on days 1, 3, and 7. A strong signal was localized in basal and suprabasal cell layers in the nonwounded area, while only the basal cell layer was MMP-9 positive in the migrating epithelial sheet. Seven days after wounding, granulation tissue exhibited an unusually strong signal for MMP-9 messenger RNA. Wound fluid contained mainly MMP-9, the amount of which was highest in two- to four-day-old secretions. None of the cytokines tested (transforming growth factor beta-1, interleukin-1 beta, basic fibroblast growth factor, tumor necrosis factor-alpha, interferon-gamma) were able to regulate MMP-2 expression in cultured wound fibroblasts. However, keratinocyte MMP-9 production was enhanced by interleukin-1 beta, transforming growth factor beta-1, and tumor necrosis factor-alpha. CONCLUSIONS During wound healing, MMP-9 is suggested to be involved in keratinocyte migration and granulation tissue remodelling. Expression of MMP-2 remains stable during wound healing.