Perioperative thromboembolism can be effectively prevented by low-dose heparin. However, its clinical benefit is limited, due to the risk of bleeding, the need for multiple daily doses, infrequent disorders of platelet function and other potential side effects. Low molecular weight heparin (LMWH) was developed with the aim that the antithrombotic efficacy of heparin could be maintained, while the risk of bleeding and other side effects would be reduced. Prior to recent studies, the anticipated clinical benefit of LMWH remained a controversial issue. We have reviewed the clinical pharmacology and the results of several prospective trials using reviparin a LMWH which has been compared with unfractionated heparin (UFH) and another LMWH. The efficacy and safety of reviparin was examined in the prevention of venous thromboembolism in high risk patients undergoing elective major abdominal and hip surgery. The results of these clinical trials show that reviparin is as effective as UFH in preventing venous thromboembolism whilst having a lower incidence of bleeding complications. Of major significance was the finding that a very low dose of reviparin, namely 1750 anti-Xa IU once daily, was found to be as effective as UFH in preventing deep vein thrombosis whilst having a significantly lower incidence of bleeding complications in patients undergoing major abdominal surgery. Reviparin has also been shown to be effective and safe as enoxaprin in patients undergoing elective hip surgery. Further clinical trials are required to test different dosage regimens as a thromboprophylactic agent in high risk patients. It is possible that reviparin and other LMWHs with similar pharmacological properties may have an important clinical benefit over earlier compounds. However, this needs to be assessed in large scale, double-blind, randomised clinical trials.