The most abundant cell type in the bronchus is fibroblasts. Human Bronchial Fibroblasts (HBF) display a mesenchymal stem cell phenotype and their principle function is to produce type III collagen, elastin, and proteoglycans of the extracellular matrix. Bronchial fibroblasts play an important role in the repair and remodeling processes following injury. The controlled accumulation of fibroblasts to sites of inflammation is crucial for effective tissue repair after injury. Either inadequate or excessive accumulation of fibroblasts can result in abnormal tissue function. For example, the excess fibroblast proliferation and collagen secretion that occurs from bronchial subepithelial fibrosis can result in airway obstruction and bronchial hyper-responsiveness. HBF cultures provide an in vitro model in the pathophysiological studies of bronchial disorders; such as bronchiectasis, bronchiolitis or bronchopulmonary dysplasia.