The protein components in concentrated bronchoalveolar lavage fluids (BALFs) from 10 healthy smokers and 10 non-smokers were analysed, using a differential quantitative method to measure bronchial secretory IgA(sIgA). In 3 volunteers the effect of increasing the volume of lavage fluid was also examined, indicating an increased recovery of each protein component but no change in the ratio of the different proteins. Albumin (Alb), alpha 1-antitrypsin, IgG and sIgA were consistently found, and IgE, C3-activator and C4 were sometimes found in BALFs, whereas, characteristically, IgM could never be detected. IgG/Alb ratio was not different from the serum value, reflecting passive transudation of IgG from the serum. However, some bronchial IgG could also be produced locally, especially in smokers, because their bronchial IgG/Alb ratio was significantly higher than in non-smokers. For IgA/Alb ratio, BALFs values were much higher than in serum, implying that most of the bronchial IgA was synthesized locally. In smokers, the amount of bronchial IgA tended to be decreased, suggesting that cigarette smoking suppresses bronchial IgA production and, hence, disturbs the local immunity of the lung.