1. Treatment of serum with chloroform results in immediate inactivation of the protease inhibitor present. 2. Following a lag period of less than one to several days, proteolytic activity begins to appear in the chloroform-treated serum. Activity increases over a period of several days and then begins to diminish gradually. At about the time when the spontaneous activity begins to diminish, the total proteolytic activity of the preparation also begins to fall until finally the two curves coincide. 3. Chloroform treatment of serum appears to result in some destruction of plasminogen because not only is the total proteolytic activity of the chloroform-treated serum less than that of the serum before chloroform treatment, but the maximum spontaneous activity that develops is only about one-half the total proteolytic activity of serum before treatment with chloroform. 4. The spontaneous activation of plasminogen which occurs following removal of inhibitor appears to be autocatalytic in nature. 5. In the presence of active plasmin, both plasmin and plasminogen are destroyed.