The urokinase pathway of plasminogen activation is involved in proteolytic degradation of various tissues, including dissolution of the extracellular matrix and basement membranes during the process of cancer cell invasion. We have studied the prognostic value of urokinase-type plasminogen activator (uPA) and type-1 plasminogen activator inhibitor (PAI-1) in tumor extracts from 106 patients with adenocarcinoma of the lung. uPA and PAI-1 levels were determined by sandwich enzyme-linked immunosorbent assays. No correlation was found between uPA and PAI-1 (r = 0.23). High PAI-1 levels were significantly associated with short-duration overall survival (P = 0.017), while uPA levels showed no significant association with overall survival. Relating the levels of PAI-1 to other prognostic factors such as stage and age, no significant correlations were found. The prognostic impact of uPA and PAI-1 were investigated together with other prognostic factors in Cox multivariate analysis. PAI-1 was found to be an independent prognostic variable for survival, the relative risks being 1.5 (low versus medium PAI-1 values (95% confidence interval, 1.2-1.8) and 2.2 (low versus high (95% confidence interval, 1.8-2.6)). In patients with stage I disease (69 patients) high levels of PAI-1 were significantly associated with poor prognosis compared to low levels (P = 0.037). These data indicate that PAI-1 is a potentially important prognostic factor in pulmonary adenocarcinoma and may as such be used to select patients with low stage and poor prognosis for adjuvant therapy subsequent to complete surgical resection.