Previous to the evaluation of fibrinolytic activity in endometrial adenocarcinoma, samples were homogenized. Fibrinolytic activity was determined on sigma bovine fibrinogen plates. In the test activated with streptokinase, .25 ml endometrial saline solution was activated with .1 ml of 500 micro/ml streptokinase solution. The mixture was incubated at 37 degrees C for 10 minutes and then placed on the fibrin plate for its evaluation. Cold and incubated plates were the same. The fibrinolytic activity was increased in the adenocarcinoma cases. A halo of white precipitate appeared but this was not present when normal endometrium was evaluated. The fibrinolytic activity of the endometrium was reduced when aminocaproic acid was added but the white halo persisted. A similar halo appeared in a case of cystic glandular hyperplasia. Results suggest that the halo might be bound to some other activity, different from the plasminogen activators' function, possibly proteases. Plates illustrate the halos.