Squamous cell carcinomas (SCCs) of the head and neck are malignant tumors with high capacity to invade and metastasize. We have examined expression of the new collagenase, collagenase-3 (MMP-13), in SCCs of the head and neck. MMP-13 mRNAs were detected in 22 of 29 SCC cell lines: in 14 of 15 primary SCC cell lines and in 8 of 14 SCC cell lines from recurrent tumors or metastases. MMP-13 mRNAs were expressed by all 6 cell lines from highly invasive primary tumors and in all 4 cell lines from small aggressive tumors. Using in situ hybridization, MMP-13 mRNAs were detected in 15 of 17 SCC tumor samples. In most tumors, MMP-13 was expressed by tumor cells at the invading front of the tumors, but in a subset of SCCs, MMP-13 mRNA was also expressed by stromal fibroblasts. No MMP-13 expression was detected in intact skin or oral mucosa. MMP-13 mRNA levels in SCC cells were enhanced by transforming growth factor-beta, tumor necrosis factor-alpha, transforming growth factor-alpha, and keratinocyte growth factor. Specific expression of MMP-13 by SCC cells in vitro and in vivo strongly suggests a role for MMP-13 in the high invasion capacity of SCC cells.