We have previously shown that the extracellular-matrix-degrading enzymes, urokinase-type plasminogen activator (u-PA), stromelysin 1, stromelysin 3, and matrilysin, may play an important role in the transition from lung preneoplasia to invasive carcinoma. Using in situ hybridization and immunohistochemistry, we analyzed serial frozen sections for the expression of these enzymes in 89 lung carcinomas including 25 neuroendocrine (NE) carcinomas (10 small-cell lung carcinomas, 7 large-cell NE carcinomas, 1 atypical, and 7 typical carcinoids) and 64 non-small-cell, non-NE carcinomas (29 squamous and 7 basaloid carcinomas, 23 adenocarcinomas, and 5 large-cell carcinomas). Proteases, except matrilysin, were more often expressed in stromal than cancer cells. In non-small-cell, non-NE carcinomas, stromal co-expression of u-PA and stromelysin 3 was seen in 80 to 90% of the tumors and was highly correlated (P < 0.0001). Stromal u-PA and stromelysin 3 expression was linked to tumor size (P = 0.01 and 0.03, respectively) and lymph node involvement (P = 0.001 and 0.02, respectively). Epithelial expression of u-PA was correlated to tumor size (P = 0.04). Epithelial expression of stromelysin 3 predominated in squamous and basaloid carcinomas (P = 0.0005) and was inversely correlated to squamous differentiation (P = 0.018). Epithelial expression of matrilysin predominated in adenocarcinomas and large-cell carcinomas (P = 0.07). In NE carcinomas including small-cell lung carcinomas, stromal expression of u-PA was correlated to lymph node metastasis (P = 0.017). Epithelial expression of all enzymes were significantly less frequent in NE than in non-NE tumors. We conclude that 1) epithelial expression of matrix proteases in lung cancer is linked to cell phenotype (NE versus non-NE, squamous versus glandular) and 2) their stromal, rather than epithelial, expression influences local metastasis.