In search of direct in vivo evidence of matrix metalloproteinases (MMPs) in periodontal tissue destruction, we studied the presence and localization of MMP-9 and neutrophil gelatinase-associated lipocalin (NGAL) in adult periodontitis (AP) and localized juvenile periodontitis (LJP) gingival tissue specimens by immunohistochemistry, and the activities of gelatinases by Western blot, enzymography, and activity measurements, using radioactive gelatin as substrate in gingival crevicular fluid (GCF) and saliva. In gingival tissue obtained from AP and LJP patients, polymorphonuclear leukocyte (PMN) 92-kDa MMP-9 and NGAL were seen in the connective tissue, but both the sulcular and the oral epithelia were consistently negative. Whereas PMNs located in the gingival blood vessels showed strictly cytoplasmic MMP-9 and NGAL immunoreactivities, in the case of PMN extravasation the staining reactions extended extracellularly. Gelatinase activities consisting mainly of 92-kDa gelatinase were increased in AP GCF relative to LJP GCF and periodontally healthy control GCF. Western blot with specific anti-NGAL antibodies revealed the presence of 25-kDa NGAL and its high-molecular-weight forms in AP and LJP GCF and saliva and in culture medium of oral keratinocytes, but not in gingival fibroblast culture medium. We conclude that extravasated degranulating PMNs are the major source of MMP-9 and NGAL in periodontitis gingiva, GCF, and saliva.