Since the early 1980s, much attention has been paid to the development of a biochemical marker for venous thromboembolism. D-dimers are derivatives of fibrinolysis and recently have been touted as a means of screening for thromboemoblism. We review the physiologic, pathologic, and chemical bases for this new test, and outline the specific D-dimer assays currently available. We conclude with a discussion of the clinical utility of D-dimer in the evaluation of patients with venous thromboembolism.