In a prospective, controlled clinical study prevention of postoperative deep venous thrombosis by low-dose heparin (Heparin Leo 5 000 I.U. subcutaneously twice daily) was compared with graded compression stockings (TED stockings, Kendall Co.). One hundred and twelve patients, admitted during a period of one year for elective major surgery, were allocated to one of the two treatment groups. In order to detect deep venous thrombosis the 99mTc-plasmin test was performed before the operative procedure and again 5 days later. Ninety-seven patients completed the study (45 patients in the heparin group and 52 patients in the stocking group). Venous thromboembolism was detected in 4 patients (8.9%) in the heparin group and in 3 patients (5.8%) in the stocking group (p greater than 0.05). In 6 patients the plasmin test was positive and one patient in the heparin group died following pulmonary embolism. It is concluded that graded compression stockings can be used as an alternative to low-dose heparin for prophylaxis against deep venous thrombosis in elective general surgery.