Byssinosis is a human disease of bronchi. Early in its course, it is symptomatically characterized by bronchospasm, i.e., chest tightness and dyspnea. Late in its course, it is characterized by abnormal differentiation in the bronchi, i.e., excessive number of mucus-producing cells with inadequate ciliated cells (1,2,3). This results in dyspnea, cough, and airway obstruction. Although no pathological observations are available for acute byssinosis, the only lesion seen at autopsy which is associated with exposure to cotton dust is the abnormal bronchial differentiation with chronic inflammation. Thus, byssinosis, in all its manifestations, appears to be purely a bronchial disease.