Phlebitis in an extremity always presents a worrisome problem to the attending doctor, and is a development of serious danger to the patient. Much interest in the study of this disease has been shown by great physicians for centuries. Gradually knowledge has accumulated relating to many facets of the problem: causative factors, pathology, preventive measures, and active treatment. Despite the immense volume of work on the subject, the condition is still a fearsome one, fraught with difficulties in treatment and, above all, prone to the development of crippling late sequelae.1, 2 All well informed doctors and nurses are aware of the measures designed to prevent venous thrombosis, including avoidance of pressure on the legs and feet, activity of the limbs, proper bandaging, elevation of the foot of the bed, early ambulation, and the like. In treatment of these patients we are all very familiar with the usual hot applications, antibiotics, anticoagulants, and vein interruption procedures. Although these methods usually result in favorable results, they are difficult to control, time-consuming, expensive, and occasionally unsuccessful.Often after control of the acute process, chronic disability persists.2 With regard to sequelae, the pathologic process is not reversed by anticoagulant therapy, and the sequelae which cause so much trouble often develop. Failure of lysis of the offending clot results in the organization of the thrombus, recanalization, and destruction of the valves. With loss of elasticity in the vein walls and destruction of the valvular system of these lower extremity deep veins, the stage for the sequelae is set. Edema persists. There is interference with skin circulation. Dermatitis and ulcer may occur. Once these changes have begun, they are virtually irreversible despite the most vigorous treatment. With vein ligation therapy, especially with the higher ligations of iliac or vena cava, similar disabling complications often arise.3-5What is needed is a more certain method of treatment of thrombophlebitis and phlebothrombosis, one which will eradicate the thrombus and allow the vein and valves to return to normal. The ideal method should be simple, successful, and less dangerous and cumbersome than existing methods.Our experience with fibrinolysin shows promise of a more effective, more rapid, and simpler method of treatment of these conditions. The method is basically the administration by infusion of a plasmin preparation (Fibrinolysin) in sufficient quantity and for a long enough period to achieve the desired result. Two cases of iliofemoral thrombophlebitis are presented below.CASE REPORTS Case 1. J. Vr., a 43-year-old female entered Roosevelt Hospital in February 1958 because of an abdominal growth. Upon examination blood pressure was 150/90. The patient was very pale, and the abdomen was filled by a huge, firm tumor arising in the pelvis and extending to the xiphoid. Other than pallor of nailbeds there was no noteworthy finding in the lower extremities.