In children with persistent respiratory symptoms despite regular anti-asthma inhalation treatment, diagnostic investigations to exclude underlying disease are warranted. 124 children were prospectively enrolled, and 24-h oesophageal pH measurement and fibreoptic bronchoscopy with bronchoalveolar lavage (BAL) were performed. BAL fluid (BALF) was processed for neutrophil counting and bacterial culture. Inflammation of the respiratory mucosa was assessed. A structural abnormality of the central airways was found in 47% of subjects (40% females). In 19% of subjects, neither anatomical anomalies nor inflamed respiratory mucosa were observed, whereas in 64%, definite macroscopic mucosal inflammation was observed. Inflammation of the respiratory mucosa was associated with a significantly higher percentage of neutrophils in the BALF: median (interquartile range) 48 (14-82)% compared with 7 (0-16)% (p<0.025). A positive BALF culture was found in 62% of the infants with mucosal inflammation compared with 25% in the group without inflammation (p<0.016). 56% of the BALF samples were positive for bacterial culture. In children with persistent respiratory symptoms, nearly half have anatomical anomalies of the central airways. In 62% of the children with mucosal inflammation, a positive BAL culture and a significantly higher percentage of BALF neutrophils were detected.