The present concept of physiologic fibrinolysis was reviewed. It was concluded that the nonspecific proteolytic activity of plasmin would essentially be limited to fibrin in vivo in view of (A) the specific adsorption of activator and of plasminogen onto the fibrin surface resulting in local generation of plasmin and (B) the fact that plasmin, adsorbed to fibrin (in contrast to plasmin in the fluid phase) largely escapes from the action of antiplasmin. The hemostatic balance in the resting condition was discussed. It was concluded that under normal conditions, systemic intravascular fibrin deposition or formation must be either nonexistent or extremely limited. On the other hand, there is considerable evidence that a limited systemic fibrinogenolysis is going on in healthy individuals and that this process can be accelerated by simple physiologic procedures, such as strenuous physical exercise.