["This study compared reticular basement membrane (Rbm) and vascular remodelling within the bronchial mucosa of subjects with chronic obstructive pulmonary disease (COPD) with those from patients with asthma, to test the 'Dutch hypothesis' of whether these are essentially the same or different pathological conditions.", 'Bronchoscopic biopsies were stained with anti-collagen IV antibody; 18 current smoking COPD, 10 symptomatic asthmatics and 13 healthy non-smoking controls were studied. The Rbm in COPD was fragmented, non-homogeneous, variable in thickness and hypervascular, whereas in asthma the Rbm was compact and homogeneous with no evidence of increased vascularity compared to controls. Length of Rbm splitting presented as percentage of Rbm length was used to measure fragmentation; it was greater in COPD than in controls and asthmatics [median (range) 20.7% (0.4-68.5) versus 5.3% (0.0-21.7) versus 1.5% (0.0-15.1), P < 0.001]. The number of Rbm vessels/mm Rbm [median (range) 10.1 (1.6-23.0) versus 4.5 (0.0-26.4) versus 4.4 (0.4-8.1), P < 0.01] and area of Rbm vessels, μm(2) /mm Rbm [median (range) 953 (115-2456) versus 462 (0-3263) versus 426 (32-2216), P < 0.05] was also increased in COPD compared to normal subjects and asthmatics.'] Are distinctive characteristics of bronchial reticular basement membrane and vessel remodelling in chronic obstructive pulmonary disease ( COPD ) and in asthma : they the same disease?