In a prospective randomized controlled study on postoperative thromboembolism, 259 patients undergoing elective general surgery, emergency general surgery, total hip replacement or hip fracture surgery were given thromboembolic prophylaxis with either a combination of dextran 70 and dihydroergotamine (DHE) or with dextran 70 alone. 500 ml dextran 70 was infused twice on the day of operation, once on postoperative days 1 and 3, and also on day 5 if the patient was still confined to bed. 0.5 mg DHE was given s.c. twice daily starting before operation and continued for 3 or 5 postoperative days. In hip fracture patients prophylaxis was started as soon as the diagnosis was made. 500 ml dextran 70 was given every other day before operation. DHE was given twice daily if so indicated from randomization. The patients were screened for deep-vein thrombosis (DVT) with the 125I-labelled fibrinogen test for 8 days and followed for one month postoperatively. In hip fracture surgery the incidence of DVT was significantly reduced by the combination of dextran 70 and DHE compared to dextran 70 alone (1/32 vs. 11/36, P = 0.003). However, this synergistic effect of DHE could not be detected in the other patient groups. Fatal pulmonary embolism did not occur. No severe side effects attributable to prophylaxis were noted in either group.