In situ zymography provides a tool to localize proteolytic activity in tissues in vivo. However, it has been difficult to discriminate between the proteases responsible for the detected activity. We used a selective tissue-permeable gelatinase inhibitor, the CTTHWGFTLC-peptide (CTT) in inflamed human gingiva. The CTT-peptide was evidenced to home, target to, and selectively inhibit the areas of gelatinolytic activity in inflamed human gingiva expressing MMP-2 and -9. Gelatinolytic activity, MMP-9 immunoreactivity, and mRNA expression as well as CD-45-positive inflammatory cells colocalized well in the inflamed human gingival connective tissue. Gelatinolytic activity corresponding to MMP-2 colocalized with laminin-5 gamma2-chain immunoreactivity and was detected in the close vicinity of the sulcular basement membrane region. Furthermore, the CTT-peptide inhibited beta -caseinolysis by human MMP-2 and MMP-9 as well as laminin-5 gamma2-chain degradation by MMP-2 in vitro. Thus, the CTT-peptide may prove to be a useful tool (i) to discriminate between gelatinolytic proteases detected by in situ zymography and (ii) to prevent MMP-2-dependent induction of epithelial cell migration and gelatinase-dependent tissue destruction in inflammatory and malignant diseases.