Clinical laboratory services are an invaluable aid to our veterinarians for the diagnosis and treatment of diseases of the horse. Abnormalities found in laboratory tests reflect the pathophysiologic changes in the body that occur with disease. These tests are always interpreted in the context of a thorough physical examination of the horse. They serve as a guide to rational therapy and also help to establish an accurate prognosis. Some clinical laboratory tests are performed in our “in house” laboratory in order to provide immediate feedback to our clinicians. Other tests are sent overnight to a reference laboratory that provides sophisticated diagnostic support in areas such as microbiology and histology.