The serine protease system has been shown to play an important role in the invasive potential of a variety of tumors. To date, however, there are little data about the expression of these proteases in esophageal carcinoma. To determine the level of expression and the significance of urokinase-type plasminogen activator (uPA) and its plasminogen activator inhibitor type 1 (PAI-1) in adenocarcinoma of the esophagus, we studied 54 tumor cases and a control group of normal gastric mucosa cases with ELISA using detergent-extracted samples. uPA and PAI-1 were significantly elevated as compared to control tissue by factors of 16 and 14, respectively. Median levels of both uPA and PAI-1 showed significant correlation with tumor pT, pN, and pM categories, whereas the presence of lymphatic invasion correlated only with the uPA content and tumor grade correlated only with PAI-1 content. Using maximally selected statistics, a cutoff value was found for uPA (2.85 ng/mg protein) but not for PAI-1, which divided the study group into significantly poorer and better survival subgroups. By univariate analysis, depth of tumor invasion (pT), lymph node involvement (pN), number of involved lymph nodes, lymph node ratio, distant nodal metastases [pM1(Iym)], lymphatic invasion, and uPA showed significant correlations with patient survival. By multivariate analysis, uPA (first rank), pN, and pM (lym) were identified as independent prognostic factors, with relative risks of 8.4, 4.1, and 4.3, respectively. In a second survival analysis method, a prognostic model was developed using classification and regression trees analysis, in which a significant difference among three patient survival groups was distinguished using the variables "number of involved lymph nodes" and "uPA content." In summary, tumor uPA content as determined by ELISA appears to be a powerful, independent prognostic factor for survival in adenocarcinoma of the esophagus.