We examined the production and tissue localization of matrix metalloproteinase-7 (MMP-7 = matrilysin) in human gastric carcinomas and analyzed the data in connection with the clinicopathological factors. Sandwich-enzyme immunoassay for the zymogen of MMP-7 (proMMP-7) showed enhanced production of MMP-7 in carcinoma tissues compared with control normal gastric mucosa. Immunohistochemical studies demonstrated that MMP-7 is localized predominantly to the carcinoma cells in 71% of the carcinoma samples (30/42 cases). The percentage of immunoreactive carcinoma cells to total carcinoma cells (positive ratio) was significantly higher in intestinal-type carcinomas (26%, median) than in diffuse-type carcinomas (3%, median) (p < 0.05). The positive ratio was markedly higher in carcinoma groups with vascular invasion (28%) or lymphatic permeation (12%) than in those without invasion (6%) or permeation (0%) (p < 0.05). It was also significantly higher in carcinoma groups with liver (49%) or lymph-node metastases (15%) than in those without metastases (6 and 2% respectively) (p < 0.05). Both proMMP-7 of 28 kDa and active MMP-7 of 19 kDa were detected in the carcinoma tissues by immunoblotting. Reverse-transcription-PCR showed specific amplification in 50% of the carcinoma cases (6/12 cases) and 8% of the normal control specimens (1/12 cases). In situ hybridization demonstrated that the carcinoma cells almost selectively express MMP-7 mRNA. These data suggest that enhanced production of proMMP-7 and its activation are implicated in invasion and metastasis of human gastric carcinomas.