Concentrations of albumin, IgG, IgA, IgM, alpha 1-acid glycoprotein, alpha 1-antitrypsin, alpha 2-macroglobulin, transferrin, haptoglobin, and coeruloplasmin were determined by radial immunodiffusion in the blood sera and bronchial washings of 8 patients without clinical, radiologic or bronchoscopic evidence of lung diseases. The local production of the proteins was calculated with a formula used by Deuschl and Johansson for the estimation of local synthesis of bronchial immunoglobulins. The formula was completed by a reduction factor established by the authors, based on their previous investigations. The calculations indicated that the individual proteins were secreted locally in various percentages of the total amount found in the secretion, as follows: IgG, 37%; IgA, 84.5%; transferrin, 44.5%, alpha 1-antitrypsin, 15.2%; coeruloplasmin, 11.3%. Local synthesis of IgM was found only in 3 patients. The alpha 1-acid glycoprotein and the haptoglobin do not seem to be secreted locally by the normal bronchial mucosa; they reach the mucus from blood only, through ultrafiltration.