We have reported previously that both urokinase-type plasminogen activator (uPA) and its type 1 inhibitor (PAI-1) are statistically significant prognostic variables in patients with high-risk breast cancer (Grondahl-Hansen et al., Cancer Res., 53:2513-2521, 1993), and we recently described that the uPA receptor (uPAR) is a prognostic marker in postmenopausal, node-positive breast cancer patients (Grondahl-Hansen et al., Clin. Cancer Res., 1:1079-1087, 1995). The present retrospective study describes the prognostic impact of uPA, its receptor uPAR, and PAI-1 in breast cancer cytosol from 111 low-risk premenopausal patients and 184 low-risk postmenopausal patients with a median follow-up of 6.0 years (range, 3.8-14.9) and 7.4 (range, 3.7-14.0) years, respectively. uPA, uPAR, and PAI-1 levels were determined by sandwich enzyme-linked immunosorbent assays, and data were dichotomized using the median value as the cutoff for calculation of recurrence-free survival and overall survival. A correlation was found between the levels of each of the three molecules. In univariate analysis, high PAI-1 was significantly associated with short overall survival in postmenopausal patients [relative risk (RR), 2.3; 95% confidence interval (CI), 1.3-4.3; P = 0.005] and shorter recurrence-free survival in both premenopausal (RR, 2.5; 95% CI, 1.3-4.7; P = 0.004) and postmenopausal (RR, 1.8; 95% CI, 1.1-2.9; P = 0.02) patients. Neither uPA nor uPAR reached statistical significance in the univariate analyses. The prognostic value of uPA, uPAR, and PAI-1 was then compared with that of other established prognostic variables by multivariate analysis. PAI-1 was an independent prognostic variable for recurrence-free survival in premenopausal patients, with a RR of 2.6 (95% CI, 1.3-5.0). For recurrence-free survival (RR, 1.9; 95% CI, 1.1-3.5) and overall survival (RR, 2.6; 95% CI, 1.2-5.7) in postmenopausal patients, PAI-1 was the only independent variable left in this group of patients. Neither uPA nor uPAR reached significance in the multivariate analysis. These data, together with previously published data on the prognostic significance of components of the urokinase plasminogen activation system in breast cancer cytosols, strongly indicate that PAI-1 is a statistically significant and independent prognostic marker in both low- and high-risk breast cancer patients.