In a double-blind, placebo-controlled study, we measured the effect of disodium cromoglycate (DSCG) on leukocyte counts, total IgE, IgG, IgA, IgM, house dust mite-specific IgE, C3, and C4 in bronchoalveolar lavage (BAL) fluid and peripheral blood in 36 atopic, perennial asthmatic subjects (DSCG 19; placebo 17). Differential cell counts on bronchial mucus were also performed. The percentage of eosinophils in bronchial mucus and BAL fluid was significantly less after DSCG. There was also a significant decrease in the concentration of total IgA (expressed as an IgA/albumin ratio) in BAL fluid after a 28-day treatment with DSCG. When the DSCG-treated patients were divided into responders and nonresponders on the basis of average daily symptom scores, the responders had significantly less bronchial mucus eosinophils, BAL eosinophils, and house dust mite-specific IgE (but not IgA) after DSCG. No significant differences in any of the measurements were observed in the nonresponders or the placebo group similarly subdivided on the basis of symptom scores. These results suggest that the efficacy of DSCG in bronchial asthma might be related to its ability to suppress the local accumulation of eosinophils and specific-IgE antibodies.