Two hundred and forty-five patients who underwent acute extensive abdominal operations were randomized into three regimens to achieve optimal prophylaxis of postoperative thromboembolic complications. All of the patients were screened by the 125I-fibrinogen uptake test for seven days and if the phlebographic findings were positive. Of 81 patients receiving low dose heparin, 12 had thromboembolism. Of 79 receiving a combination of low dose heparin and graded compression stockings, two had thromboembolism, and of 85 receiving a combination of dextran and graded compression stockings, 13 had this complication. This difference is significant in favor of the second treatment (p = 0.013). It is concluded that the combination of low dose heparin and graded compression stockings is an effective way to prevent thromboembolism after acute abdominal operations.