The value of low-molecular-weight heparin in the treatment of patients with pulmonary embolism or previous episodes of thromboembolism was studied in more than 1000 patients in a multi-institutional study. Randomly assigned patients with symptomatic venous thromboembolism were treated with fixed-dose, subcutaneous, low-molecular-weight heparin or adjusted-dose, intravenous, unfractionated heparin. Treatment with oral coumarin was started concomitantly and continued for 12 weeks. The outcome events studied included recurrent venous thromboembolism, major bleeding, and death. Fixed-dose, subcutaneous, low-molecular-weight heparin proved as effective and safe as adjusted-dose, intravenous, unfractionated heparin in all categories.