The lysis and aspiration of a clotted hemothorax by means of an effective enzymatic agent is highly desirable. Various enzymes have been used for this purpose but alt have certain disadvantages. Trypsin has an irritative effect of pleural pain on injection and often shows a toxic reaction due to the enzyme or breakdown of protein products.’ The inhibitor (antitrypsin) normally present in the serum or exudates rapidly increases in concentration after the use of trypsin.� This may require an increasing dosage of trypsin with successive treatments. Streptokinase-streptodornase acts primarily as an activator and depends on plasminogen in the wound exudates.� Occasional pyrogenic reactions are encountered with this enzyme.4 Inhibitors to streptokinase are also present in many patients who have had streptococcal infections.5 The proenzyme, profibrinolysin, circulates in human and animal plasma. Proenzyme becomes activated during life or after death of the organism. Some of the known activators are streptokinase, staphylokinase, cytofibrinolysokinase, epinehprine, chloroform and potassium cyanide. Dastre#{176} noted the proteolytic substance of blood serum and named this fibrinolysin. Loomis isolated the active proteinase in 1946.� Fibrinolysin is an euglobin, soluble in saline and when mixed with antibiotics loses little activity. Fibrinolysin attacks only fibrin, fibrinogen or