Thromboembolism is a major cause of morbidity and mortality in patients with spinal cord injury. The prevalence of DVT approaches 100%, and 1 to 2% will die of PE. Following injury, there is hypercoagulability as reflected by an increase in von Willebrand factor activity and antigen, and increased platelet reactivity to collagen. Thrombosis usually occurs 1 to 3 weeks after injury, with a peak between days 7 and 9. Intermittent calf compression boots reduce the frequency of thrombosis to 40%, and the addition of aspirin, 300 mg twice daily, and dipyridamole, 75 mg thrice daily, decrease this further to 25%. In an attempt to provide more effective prophylaxis, a further trial was conducted using heparin. Twenty-nine patients were randomized to receive 5000 U subcutaneously every 12 hours and compared with an equal number of patients treated with doses of heparin adjusted to prolong the APTT to 1.5 times control values; the mean dose was 13,200 U every 12 hours. Thromboembolism occurred in 9 (31%) of those on the fixed dose (6 DVT and 3 PE) and only 2 (7%) on the adjusted dose (p less than 0.05); however, 7 (24%) of the patients receiving the higher doses of heparin had bleeding compared with none of those on the fixed dose (p less than 0.02). Most recently, we have compared the safety and effectiveness of a low molecular weight heparin (Logiparin, Novo) with standard heparin. The former was given once daily in a dose of 3500 anti-Xa units, and the latter was 5000 U every 8 hours, both given subcutaneously.(ABSTRACT TRUNCATED AT 250 WORDS)