OBJECTIVE: To quantitatively assess the efficacy and safety of published randomized trials comparing subcutaneous heparin with continuous intravenous heparin for the initial treatment of deep vein thrombosis. DATA IDENTIFICATION: Studies published between January 1986 and April 1991 were identified through computer searches of the MEDLINE database and through reviews of the Science Citation Index, Current Contents, proceedings and abstract books, and references cited in the identified articles. Complete manuscripts were obtained from the authors if only abstracts were available. STUDY SELECTION: Eight clinical trials were identified that compared subcutaneous with intravenous heparin administration in patients with venographically confirmed deep vein thrombosis. DATA EXTRACTION: Each study was independently analyzed for the percentage distribution of thrombosis, the method of outcome measurement, and the heparin dose. The methodologic strength of each study was assessed using predefined standards for the proper evaluation of a therapeutic intervention with particular emphasis on the type of patient allocation and objective measurements. RESULTS OF DATA ANALYSIS: The overall relative risk for efficacy (defined as prevention of extension and recurrence of venous thromboembolism) of subcutaneous compared with intravenous heparin treatment was 0.62 (95% CI, 0.39 to 0.98), whereas for safety (defined as major hemorrhage) it was 0.79 (CI, 0.42 to 1.48). CONCLUSIONS: The results of our meta-analysis indicated that heparin administered subcutaneously twice daily in the initial treatment of deep vein thrombosis is more effective and at least as safe as continuous intravenous heparin administration. Administration of heparin subcutaneously may simplify patient treatment and could facilitate home treatment.