Abstract 1.1. During the past decade the indications for anticoagulant therapy have been clarified. They are listed herein. 2.2. In view of the reduction in both death rate and in the incidence of thromboembolic complications following coronary thrombosis with myocardial infarction with the use of anticoagulants in mild and moderately severe cases, the position that their use should be reserved solely for those patients who are severely ill at onset does not appear justified. This because, despite apparent mildness during the first day or two of the disease, the future course is difficult or impossible to predict with certainty and because the first complication may produce death, more serious illness or permanent disability. 3.3. Recent evidence favors the increased use of anticoagulants during more severe periods o congestive heart failure. 4.4. Newer anticoagulants are now rapidly being developed which generally can be classified as acting similarly to heparin or to dicumarol. 5.5. The clinical facts regarding each of the better known anticoagulants, including their advantages and disadvantages, have been outlined. 6.6. More complete experimental studies should be carried out before crystalline trypsin should be released for general clinical use. 7.7. The final decision whether to use anticoagulants or not, and which ones to use in a specific patient, must rest with the physician responsible for his care. 8.8. Among the important factors to be considered in making this decision are: (1) The diagnosis and condition of the patient; (2) the presence of any coincidental problem requiring caution or contraindicating their use; (3) the sound evidence indicating anticoagulant therapy under these particular circumstances; (4) the qualities of the specific anticoagulants under consideration; (5) the availability of accurate prothrombin and coagulation time tests; (6) the availability of vitamin K and K 1 , and transfusions for emergency use; and, perhaps of greatest importance, (7) the conscientiousness, and skill in this particular field, of the physician who is responsible for their use.