Plasminogen-activating activity (PAA) was determined on cytosols prepared from human breast cancers. Coincident assays of steroid-binding proteins were obtained for 119 patients. Significant positive correlations were found between PAA and binding of: 1) estrogen (P less than 0.01), 2) progestin (P less than 0.001), and 3) triamcinolone (P = 0.01). Stepwise regression analysis indicated that variations in the levels of progestin binding accounted for 17% (P less than 0.01) and variations in the levels of triamcinolone binding for 3% (P = 0.05) of the variation observed in PAA. Use of the median value of each assay to discriminate positive from negative values accentuated the positive correlation between PAA and binding of 1) estrogen (P = 3.9 X 10(-5), 2) progestin (P = 1.9 X 10(-4), and 3) triamcinolone (P = 6.1 X 10(-5). Preliminary results suggested that values of PAA equal to or greater than the median correlated positively with response to treatment by hormone manipulation (P = 0.0549). Possible significance of these observations was discussed.