The incidence of deep venous thrombosis (DVT) was studied by the 125I-fibrinogen technique in 70 patients who had had major abdominal operations and who were wearing graduated static compression stockings on one leg, the patient's other leg being used as a control. In the whole group 7 patients developed bilateral DVT, 19 patients developed unilateral DVT in the control leg and only one patient developed unilateral DVT in the stockinged leg. The difference between stockinged and control legs was highly significant (P = 0-0003). In the 19 patients with malignant disease the incidence of DVT in the stockinged leg remained significantly less (P = 0-037). It is concluded that graduated static compression stockings do reduce the incidence of postoperative deep venous thrombosis.