In a prospective, randomized study on 114 patients undergoing major abdominal surgery, the prophylactic effect of dihydroergotamine (DHE) combined with low-dose heparin (LDH) against postoperative deep vein thrombosis (DVT) was compared with that of peroperative intermittent pneumatic calf compression (IPCC). The additive effect of graduated pressure stockings was also studied, by randomizing a stocking to the right or left leg in each patient. The 125I-fibrinogen test was used to diagnose DVT. The incidence of postoperative DVT was significantly lower in the DHE-LDH than in the IPCC group (4% v. 19%). In the IPCC group the incidence of postoperative DVT was equal in legs with and without stocking. The study thus indicated that DHE-LDH is more effective than peroperative IPCC in preventing DVT after major abdominal surgery, and that graduated pressure stockings do not enhance the prophylactic effect of peroperative IPCC.