In an attempt to define the composition of normal bronchial secretions, bronchial washings were obtained from normal areas of the lung in six patients. An analysis of proteins in the washings was carried out by crossed immunoelectrophoresis. The proteins detected were derived mainly from plasma and a very low content of secretory proteins was found. The composition of bronchial secretions and bronchial washings from a bronchitic patient was established and compared by crossed immunoelectrophoresis and gel filtration. The most important components were IgA, alpha1-antichymotrypsin and alpha1-antitrypsin, all of which are defense factors for the respiratory tract.