A number of clinical trials have recently demonstrated that anti-coagulant drugs such as Warfarin, are highly effective at preventing strokes and heart attacks in at-risk population groups. However, these drugs can cause uncontrolled bleeding and other undesirable side effects. Thus, frequent monitoring of blood coagulation rates by prothrombin time tests is required for safe treatment. This requires the patient to visit a clinic every few weeks for testing, at considerable expense and inconvenience. The availability of a simple, accurate, low cost home test would facilitate wider use of anti-coagulant treatments and potentially improve the standard of care for anti-coagulated patients. This proposal will explore technology that would enable such home tests. It is based upon combining the technology of Chromogenic Thrombin substrates (which enable simple prothrombin time tests) with the dry reagent technology commonly used to make low cost strip/meter based home blood glucose tests for diabetics. Chromogenic Thrombin substrates with the specificity and optical characteristics appropriate for these tests will be synthesized, and incorporated into prototype reagents. The properties of these reagents will be evaluated with a prototype meter. The performance characteristics of the system will be assessed in comparison studies with clinical materials from UCSF.