In a prospective, randomized, double-blind investigation of anticoagulant agents for prevention of deep vein thrombosis in patients undergoing operations at the lumbar-vertebral disc, 179 patients were randomly allocated to two groups. 87 patients received a fixed combination of low-molecular weight heparin 1,500 U-aPTT plus dihydroergotamine 0.5 mg (LMWH/DHE) once a day and additionally one injection of placebo per day, 92 patients received a fixed combination of sodium heparin 5,000 U plus dihydroergotamine 0.5 mg (HDHE) twice a day. Treatment was initiated two hours preoperatively in both groups and continued for at least seven days. Deep vein thrombosis (DVT), detected by the 125Iodine-labelled fibrinogen uptake-test, occurred in four patients treated with LMWH/DHE and in three patients with HDHE. In all seven patients phlebography was performed, confirming the diagnosis of DVT in one patient of the LMWH/DHE group and in two patients of the HDHE group, only. No increased bleeding was found in either group. Especially no neurological complications caused by epidural bleeding were observed. We therefore recommended to treat routineously all patients undergoing operations at the vertebral disc with antithrombotic agents. The advantages of the once daily regimen with low-molecular weight heparin include better patients' acceptance and less nursing time.