A tracheal wash is a diagnostic technique performed to collect samples from the trachea. It involves passing a sterile saline solution into the trachea through a tube inserted via endoscopy. The fluid is then withdrawn and analyzed for cells, bacteria, viruses, and other components that can indicate respiratory diseases such as bacterial infections, viral infections, and allergic airway diseases (equine a sthma). Tracheal wash is valuable for diagnosing conditions affecting the upper respiratory tract and guiding treatment decisions in horses.