Our understanding of the pathogenesis of asthma has benefitted as a result of bronchial endoscopic techniques linked to studies of bronchoalveolar lavage (LBA) and bronchial biopsy. By using modern biochemical and immunohistochemical methods as well as ultrastructural studies we are better able to specify the importance of bronchial inflammation. Currently we underline the role of epithelial lesions and of intraepithelial lesions and sub-basal inflammation. The responsibility of eosinophils in the epithelial disorder has been proved in vivo by the evidence of cationic protein found both in the LBA liquid and by the tissue localisation thanks to immunological markers. An understanding of the infiltrates and of the state of cellular activation in situ constitutes an initial step in the comprehensive of inflammation; however, these studies do not yet allow us to fully understand the mechanisms of regulation and also the trigger factor in cellular dysfunction which may be the cause. The pseudo-thickening of the basal membrane and sub-epithelial fibrosis are poorly understood, but is probably involved in epithelial repair. The histopathological mechanisms which underly the bronchial aging are equally poorly understood. In the future a better understanding of these problems of neuro-inflammatory disturbances and of epithelial permeability should facilitate the therapeutic approach.