Von Willebrand factor (vWF) is a glycoprotein which plays an integral role in primary hemostasis (blood clotting). It interacts with various receptors on both the damaged blood vessel surface and the circulating platelets in order to form a platelet plug. In the absence of sufficient vWF concentration or function, primary hemostasis is impaired creating clinical signs such as hemorrhage from mucosal surfaces and excessive bleeding after surgery or trauma. To diagnose von Willebrand Disease (vWD), determination of both vWF concentration and functional properties are important. The current gold standard test is the von Willebrand factor antigen concentration (vWF:Ag) test. This test can clearly define many of the type I and all of the type III von Willebrand trait positive dogs, but can leave some diagnoses unclear. In addition, this test is not very effective for identifying type II disease as it is a functional rather than a quantitative deficiency. DNA testing is also currently available, and while useful for making breeding decisions, its availability is limited to specific breeds and it cannot predict the risk of hemorrhage. The object of our current research is to investigate the value of additional tests as part of a newly developed diagnostic profile for improved characterization of vWD patients. This profile examines the concentration and function of vWF as well as an overall hemostasis assessment. As part of this investigation a Collagen Binding Assay (CBA), not previously available to canine patients, is being validated for possible routine laboratory use. Additional profile components include hematocrit, platelet count, partial thromboplastin time, platelet aggregation test and vWF antigen concentration will also be included in the study.