Ovarian remnant syndrome (ORS) is a challenging condition to diagnosis in dogs owing to the limitations of currently available diagnostic tests. Anti-Müllerian hormone (AMH) is a product of the ovaries that has been shown to accurately distinguish between spayed and intact dogs when measured in blood serum. Whereas the utility of AMH for the diagnosis of ORS is strongly supported by our preliminary data, this supposition requires definitive research. To this end we will recruit referring veterinarians to participate in a study to firmly validate AMH for the diagnosis of ORS. Microscopic confirmation that surgically removed specimens are ovarian remnants is crucial to our goal. This award will support the histopathological analysis of specimens that are sent to us following AMH testing. For all canine AMH results reported from our diagnostic laboratory, we will invite the referring veterinarian to participate in the study by providing a detailed history and by shipping any surgically removed tissues for histological exam. Because we have identified a few cases of canine ORS for which the AMH test was negative but the progesterone (P4) concentration was consistent with the presence of ovarian luteal tissue, we will determine if AMH+P4 is a better test than AMH alone. For those veterinarians who do not request a P4 test, our diagnostic endocrinology lab will cover the cost of measuring P4 in these instances. Overall, we expect this study will definitively confirm that AMH+P4 is an excellent test for the diagnosis of canine ORS.