For years, anticoagulant therapy has been part of the long-term treatment of many patients who have suffered a myocardial infarction. Early reports were enthusiastic and implied that the use of anticoagulants reduced the incidence of recurrent myocardial infarction and diminished the death rate. McMichael and Parry1have emphasized that there are two difficulties in interpreting these reports. One problem is the absence of a control group of patients selected at random. Another is an inadequate number of patients. The present Veterans Administration study was begun in 1957 because of a great need for reassessment of long-term anticoagulant therapy. This is a preliminary report of results of the study up to Oct 1, 1964. The study will continue for another 13 months. No patients have been added since Nov 1, 1963. Methods The original group of investigators consisted of representatives from eight VA hospitals, but has since been expanded to