Chronic inflammatory changes in the bronchial mucosa have been well documented in patients with established asthma. Much less is known of the changes, which occur in the airways of children early in the evolution of their disease with most of the information based on indirect markers of inflammation only. We evaluated markers of inflammation and tissue re-modelling in bronchial biopsies from children with early respiratory symptoms before a clear clinical diagnosis of bronchial asthma could be made. We examined bronchial biopsies performed in 27 children between the ages of 1.2 and 11.7 yr who were bronchoscoped for a clinical indication because of recurrent or chronic respiratory symptoms. The patients were re-evaluated 22-80 months after the original bronchoscopy to determine whether or not they had subsequently developed bronchial asthma. There were more eosinophils in the bronchial mucosa (129.4 vs. 19.1 cells/mm2 of lamina propria, p <0.001) and the thickness of the subepithelial lamina reticularis was greater (4.65 vs. 3.72 microm, p=0.044) in children with bronchial asthma diagnosed at follow-up, compared with the children who did not progress to asthma. Eosinophilic inflammation and airway re-modelling occur early in the natural history of bronchial asthma and are present even before asthma would be diagnosed based on clinical symptoms. Recognition of these changes and their significance for clinical disease should emphasize the need for timely detection and diagnosis of asthma in children to facilitate the early introduction of anti-asthma therapy.