In 110 high-risk patients undergoing total hip replacement the antithrombotic efficacy and safety of a single daily injection of 1500 aPTT-U low-molecular-weight heparin plus 0.5 mg dihydroergotamine (Embolex) was, in a double-blind study, compared with a twice daily administration of 5000 IU of the heparin-dihydroergotamine combination Heparin-Dihydergot. Deep vein thrombosis diagnosed with phlebography occurred in 9.6% in the Embolex-group and in 25% in the Heparin-Dihydergot-group. Intra- and postoperative blood loss and blood replacement were similar in both groups. Therefore, and on account of the single daily administration, Embolex offers at least the advantage of improved compliance of the patients and reduced workload of the nursing staff.