disease condition in horses in which blood appears in the airways during and after strenuous exercise. More than 80 percent of racehorses, including Thoroughbreds, Standardbreds, and American Quarter Horses, are affected to varying degrees. The condition can compromise racing (horse racing) performance. Affected horses are termed “bleeders,” but rarely is blood discharged from the nostrils. Endoscopic observation of blood in the trachea provides a positive diagnosis. The cause of bleeding is believed to be rupture of pulmonary capillaries as a result of high inflation and vascular pressures in the lungs during strenuous exercise. No specific treatment is available, but the diuretic furosemide (Lasix) appears to reduce the severity of hemorrhage, possibly by reducing pulmonary blood pressure, an action unrelated to its diuretic effect.