1. Thrombi were produced in the marginal vein of the ear of rabbits with the use of either thrombin or sodium morrhuate. Sodium morrhuate was found to be most dependable.
2. Plasmin given intravenously with an average dose of 10 to 15 ml. per Kg. was effective in producing a complete intravascular lysis in all instances where the thrombus was less than 24 hours old, and a partial or total lysis in the great majority of animals with thrombi over 24 hours old. This lysis took place within 1 to 2 hours after the injection of plasmin.
3. The intravenous use of plasmin is shown in rabbits to be nonlethal and nontoxic.