The broncho alveolar lavage provides information in the diagnosis of lower airway diseases. Often it is not possible to determine a definite diagnosis with material gained by endoscopy of the trachea. Especially in the diagnosis of Equine Asthma the BAL is the superior method. During a BAL sterile saline solution is carefully given in the bronchia to then be retrieved again. This fluid is then centrifuged with a special method and the supernatant examined further. Because with this method cells from the bronchi and further down can be examined it is superior to the common examination of tracheo bronchial fluid alone. It is always best to perform an endoscopy of the airways before to examine where the problem is coming from and make a diagnosis together with a BAL if feasible.