The objectives of our study were; (i) to investigate the expression of P/S cell markers CK5, CK14 and p63 in bronchial explants and BEC cultures outgrown from explants obtained from smokers without COPD and patients with COPD, (ii) to examine explants and cultures for changes in the expression of P/S markers as the number of outgrowths increased, (iii) to investigate the effect this has on the number of BECs outgrown from explants. The gene discussed is KRT5; the disease is chronic obstructive pulmonary disease.