The function of granulocytes was evaluated in bronchoalveolar lavage fluid (BALF) in 25 patients with bronchial asthma. In 8 healthy subjects, BALF contained 87.0% macrophages, 12.1% lymphocytes, 0.6% neutrophils, 0.3% eosinophils and 0% basophils. The arylsulfatase (AS)/alb ratio was 6.2(μg/mg). In asthmatic patients, BALF contained 57.1% macrophages, 13.2% lymphocytes, 8.6% neutrophils, 21.0% eosinophils and 0.1% basophils. The AS/alb ratio was 9.8 (μg/mg). These patients had a much higher number of eosinophils and neutrophils than healthy subjects. An increased number of eosinophils was found in BALF of atopic type asthma patients, and an increased number of neutrophils was found in BALF of intractable asthma patients. An increased AS/alb ratio was closely related to serum IgE levels and peripheral eosinophilia. A moderately higher AS/alb ratio was found in atopic patients than in healthy subjects or non-atopic patients. There was a relationship between the AS/alb ratio and the percentage of eosinophils and/or number of eosinophils in BALF. An inverse, but insignificant, relationship of a high AS/alb ratio to the degree of peripheral airway obstruction was found. In conclusion, analysis of cells and enzymes in BALF is considered to be useful for the explication of the pathogenic and regulatory mechanisms of bronchial asthma.