DESCRIPTION: (Investigator's abstract) An assay for heparin in blood and/or plasma that is based on its mechanism of anticoagulant action is proposed. This assay is designed to be free of the limitations of current assay methods such as variability in patient plasma coagulation components, oral anticoagulation, and simultaneous use of substances such as aprotinin in conjunction with heparin. Heparin will be determined as the complex between heparin and the serine proteinase inhibitor, antithrombin. Heparin, which catalyzes proteinase inactivation will be measured from its ability to increase the rate of inactivation of Factor Xa and/or thrombin. Currently it is estimated that more than 30 million heparin assays are performed worldwide each year. Accurate monitoring of heparin during its use in surgical procedures, particularly those that are complicated by requiring extracorporeal circulation, and more accurate determinations of the amounts of neutralizing agent required post-operatively can reduce the mortality and morbidity associated with such procedures. The book-sized device will be designed and developed that is intended for general clinical use, i.e. in the laboratory, at the point of care and in the surgical theater. PROPOSED COMMERCIAL APPLICATION: The need for heparin monitoring is well established. A simple, more accurate and robust method without the limitations of current methods and devices will fill the need for better heparin monitoring.