The effect of prolonged exercise on the components of the blood fibrinolytic enzyme system.

1. The levels of the blood components of the fibrinolytic enzyme system were measured before, during and after a 4 hr period of exercise in eight subjects.2. Mean plasminogen activator level rose progressively over the first 3 hr with little further change during the 4th hr of exercise. Following the period of exercise there was a rise in a circulating anti-activator which was still present 20 hr after completion of the exercise.3. There was no alteration in the mean blood level of plasminogen, fibrinogen, anti-plasmin or a serum inhibitor of plasminogen activation during or following the exercise.4. The significance of the findings in relation to the mechanism of interaction of the components of the fibrinolytic system is discussed.