Immunoglobulins and histamine were estimated in bronchoalveolar lavage fluid (BALF) of 25 patients with bronchial asthma, 7 patients with hypersensitivity pneumonitis, 8 patients with sarcoidosis and 3 patients with bronchiolitis. In 8 healthy subjects, relation levels of immunoglobulins and histamine in BALF were: IgG/alb ratio, 0.28±0.17 (mg/mg); IgA/alb ratio, 0.19±0.15; IgM/alb ratio, 0.01±0.01; IgE/alb ratio, 0.36±0.29×10(2)(IU/mg), and His/alb ratio, 0.67±0.29 (ng/mg). In asthmatic patients, the relation levels of immunoglobulins and histamine in BALF were: IgG/alb ratio, 0.26±0.21; IgA/alb ratio, 0.11±0.06; IgM/alb ratio, 0.01±0.01; IgE/alb ratio, 0.89±0.99×10(2), and His/alb ratio, 1.38±0.84. These patients showed a moderately higher His/alb ratio than healthy subjects. The increased His/alb ratio was closely related to immediate skin tests and serum IgE levels, especially in atopic patients. An inverse relationship was noted between an elevated IgE/alb ratio and/or His/alb ratio and the degree of peripheral airway obstruction. There was a relationship between an elevated IgG/alb ratio and peripheral airway obstruction, although there was no significant relationship between immunoglobulins/alb and/or His/alb ratios and the results of pulmonary function tests. Somewhat higher IgG/ alb and IgM/alb ratios were found in the patients with hypersensitivity pneumonitis than in the healthy subjects, although significantly higher ratios were not observed in patients with sarcoidosis or bronchiolitis. In conclusion, the estimation of immunoglobulins and histamine in BALF is considered to be useful for the explication of the pathogenic mechanism of bronchial asthma.