Human and dog bile was tested on standard heated and unheated fibrin plates and appeared to contain a heat-resistant activator of plasminogen. This phenomenon, however, was due to a simple solution by bile salts of fibrin s, formed in the absence of Ca. Fibrin i, formed in the presence of Ca and fibrin stabilizing factor was resistant to solution by bile salts. It is suggested that fibrin i be used for tests for fibrinolytic enzymes.