Assessment of airway wall remodeling in asthma is difficult in vivo. The thickness of deposited extracellular matrix proteins below the epithelium, the reticular basement membrane, can be assessed by bronchial biopsy of proximal airways. The aim of this study was to determine the relationship between the thickness of the reticular basement membrane in a sample equivalent to a central airway biopsy and the dimensions of the airway wall measured on transverse sections of both central and peripheral airways. Large and small cartilaginous and membranous airways from persons who had died from asthma (fatal asthma, n = 5) or from nonrespiratory causes with asthma (nonfatal asthma, n = 5) or without asthma (control subjects, n = 5) were studied. Reticular basement membrane thickness correlated with the percentage of smooth muscle, submucosal mucous gland, and inner wall area (p < 0.05) in large cartilaginous airways, and with inner wall area and area of smooth muscle (p < 0.01) in small cartilaginous airways, but was not related to airway wall dimensions in membranous airways. These findings show that reticular basement membrane thickness of central airways, which may be assessed by endobronchial biopsy, is correlated with airway remodeling in cartilaginous airways but not with airway wall dimensions of membranous airways.