Airway-wall remodeling leading to thickening of the bronchial wall in asthma has been invoked to account for airflow obstruction and increased bronchial reactivity to provocative stimuli. Bronchial-wall changes characteristic of asthma are thought to include increased vascularity with vasodilatation. The contention that inflammatory mediators cause bronchial vasodilatation and that growth factors may induce increased vascularity is based on little structural evidence. We took bronchoscopic biopsies from the major airways of 12 subjects with mild asthma and 11 control subjects, and evaluated bronchial vessel numbers and size, using computerized image analysis after staining for type IV collagen in vessel walls. The airways of asthmatic subjects were significantly more vascular (17.2 +/- 4.2 versus 10.3 +/- 1.9%, p < 0.001), with more vessels (738 +/- 150 versus 539 +/- 276 vessels/mm2 [mean +/- SD], p < 0.05) than those of the controls. There were significantly more asthmatic bronchial than control vessels with a cross-sectional area greater than 300 microns2 (19.4 versus 12.7%, p < 0.05). These findings provide the first confirmatory evidence that bronchial biopsies from patients with mild asthma are more vascular than those of normal controls, that there are more vessels in asthmatic airways, and that asthmatic bronchial vessels are larger than controls.