Plasma level of IgG autoantibodies to plasminogen was measured by ELISA in patients with benign prostatic hyperplasia (n=25), prostatic cancer (n=17), lung cancer (n=15), and healthy volunteers (n=44). High levels of IgG to plasminogen were found in 2 (12%) of 17 healthy women, in 1 (3.6%) of 27 specimens in a healthy man, in 17 (68%) of 25 specimens in prostatic cancer, in 10 (59%) of 17 specimens in lung cancer, and in 5 (30%) of 15 specimens in benign prostatic hyperplasia. Comparison of plasma levels of anti-plasminogen IgG by affinity chromatography showed 3-fold higher levels in patients with prostatic cancer vs. healthy men.