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The high-resolution computed tomography (HRCT) studies for bronchial asthma (BA) have revealed abnormal radiologic findings such as bronchial wall thickening, bronchiectasis, emphysema and mosaic pattern of lung attenuation. But the clinical significance of these findings are not yet clarified. In this study, we quantified the bronchial wall thickness and evaluated HRCT features in 57 BA subjects (338 bronchi) who had precipitating factors of irreversible airway remodeling, 19 COPD subjects (70 bronchi) and 10 healthy subjects (23 bronchi). Then we correlated HRCT findings with the clinical features, pulmonary functions and methacholine PC20 (PC20M) and studied their clinical significance. The bronchial wall for BA was about 1.48 mm thicker than that for COPD and about 2.34 mm thicker than for healthy controls (p < 0.0001, respectively). But the individual mean ratio of bronchial wall thickness to luminal diameter (BWT/LD) in asthmatics did not correlate with the clinical features, lung functions and PC20M. Abnormal HRCT findings, such as bronchiectasis (17.5%), emphysema (5.3%) and mosaic pattern of lung attenuation (17.5%) were found in BA. These findings were more common in BA with moderate to severe airflow limitation (FEV1 < 80%, p < 0.05) and patients with these changes had a more prolonged history of asthma (p < 0.05). PC20M was higher in BA with these abnormal changes (p < 0.001) but these patients' FEV1 (p < 0.05), FEF25-75 (p < 0.05) and specific airway conductance (p < 0.05) were lower than those having BA without such findings. In this study we showed that the bronchial wall was more significantly thickened in BA but that it did not correlate well with the clinical features, lung functions and PC20M. Additionally, patients having BA with abnormal airway and air space HRCT findings had a prolonged history of asthmatic symptoms, loss of lung functions and decreased bronchial hyperresponsiveness. These results suggested the possibility that HRCT can be used for the differentiation of BA from COPD or healthy controls. Furthermore, patients having BA with abnormal HRCT changes demonstrate poor lung function and less hyperreactive bronchi than those without. We concluded that HRCT may be useful for the prognosis and treatment of bronchial asthma cases who have the precipitating factors of irreversible airway remodelling.