The elimination of iodine‐labelled fibrinogen was followed in 3 groups of dogs after: 1. thromboplastin infusion, 2. simultaneous infusions of thromboplastin and epsilon aminocaproic acid (EACA), and 3. simultaneous infusions of thromboplastin and Trasylol. Platelet count, fibrinogen concentration, radioactivity in plasma and in fibrinogen as well as hematocrit were determined. Thromboplastin caused changes of the same type as those previously obtained with thrombin, indicating the development of a fibrinolytic process, secondary to intravascular coagulation. The secondary changes were effectively blocked by pretreatment with EACA and Trasylol. The incidence of and mortality in thromboembolism suggest some anticoagulant effect of Trasylol. The antifibrinolytic activity of Trasylol is much stronger than the anticoagulant one. EACA too, seems to give some protection against thromboplastin‐induced coagulation.