Dogs with abnormalities of platelet function may have bleeding complications post-operatively. The ability to evaluate platelet function and to test dogs prior to surgery could prevent morbidity and mortality due to bleeding complications. An index case (16 month old female spayed Newfoundland) presented to our hospital with a blood-filled abdomen following an uncomplicated spay operation. Standard coagulation testing of this dog was within normal limits. Similar post-surgical bleeding events have subsequently been found in three Newfoundland dogs closely related to the index case. Normal clotting consists of a three-part process: activation of platelets, propagation of the platelet response and eventual aggregation of platelets to form a clot and seal leaks in blood vessels. Our laboratory has extensive expertise in platelet physiology, and has developed a series of tools that allow us to explore all three phases of platelet activation and coagulation. Platelet physiology and function will be studied in Newfoundland dogs with documented bleeding disorders. These results will be compared to similar testing in related, non-affected Newfoundland dogs as well as unrelated, non-affected Newfoundland dogs (control population).