It is not at all rare to observe longitudinal folds of the bronchial mucosa during bronchoscopic examinations but no studies in particular concerning their clinical significance have appeared, perhaps because their presence is easily overlooked during routine procedures. In reviewing a serier of color slides taken in 250 cases during routine endoscopic procedures, distinct longitudinal folds of the bronchial mucosa were found in 40 cases (16%).The clinical data in these 40 cases were then examined to discover if there were any signs or symptoms in common that might throw light on the clinical significance of these mucosal folds. The following facts were revealed:Most of the cases were male patients (29 cases or 72%) over middle age and many of them were smokers over the age of 50.They complained chifly of cough, sputum, respiratory disorder (shortness of breath, breathing difficulty) and low-grade fever, and in many of these cases these symptoms had been present for long periods.They were found to suffer from chronic bronchitis, pulmonary tuberculosis, bronchiectasis, asthma, emphsema, lung cancer or other diseases in which cough is one of the cardinal symptoms.The folds in the mucous membrane were observed more often near the bifurcation of the lobular bronchi or on the bronchial walls of the upper lobe bronchi and superior and basal branches. The chief findings were hyperemia of the bronchial mucosa, swelling, mucoid and frothy secretions, and frothy secretions, and constriction and deviation of the bronchi.A noteworthy observation on bacteriogical examination of the secrations was the high rate of detection of fungus, which was found in many of those that had difficulty in expectorating.Pathohistologically, cytologic examination of the secretions revealed no distinctive findings other than the presence of eosinophils in one asthmatic patient. Examination of biopay specimens and an autopay case demonstrated definite proliferation and thickening of longitudinal elastic fibers in the bronchial mucosa.On the basis of these observations, it is speculated that the prominent folds of the bronchial mucosa seen most often in those that suffer from cough, sputum and breathing difficulty are principally caused by functional proliferation and thickening of the submucosal longitudinal elastic fibers due to persistent coughing spells.