The role of transforming growth factor beta1 (TGF beta1) in airway remodeling in asthma and chronic obstructive pulmonary disease (COPD) has not been fully described. To evaluate the possible pathogenetic role of TGF beta1 in asthma and COPD, immunohistochemical expression of TGF beta1 was described in bronchial biopsies from patients with asthma and COPD compared with healthy individuals. Twelve subjects with asthma, 13 subjects with COPD, and 10 healthy individuals enrolled in the study. Bronchial biopsies were stained with hematoxylin and eosin and anti-TGF beta1 antibody. As a result, immunoreactive TGF beta1 was mainly localized in association with connective tissue in all groups. The staining intensity was not statistically different among the groups in bronchial epithelium, whereas it was significantly higher in the group of asthma in the submucosa. Because there is evidence showing a significant increase of staining intensity in the submucosa from asthmatics but not from subjects with COPD, we may conclude that TGF beta1 may play a significant role in pathogenesis of asthma but not in COPD.