The effect of premedication with cromolyn 40 mg on the bronchial response to inhaled carbachol was investigated in four atopic and four non-atopic subjects with mild asthma. Paired carbachol inhalation tests were carried out on consecutive days in a double-blind fashion following randomized premedication with cromolyn or placebo. Bronchial sensitivity was expressed as the log dose of carbachol provoking a 15% decrease in FEV1 (log PD15 FEV1) or a 30% decrease in FEF25-75 (log PD30 FEF25-75). The mean log PD15 FEV1 was significantly greater following cromolyn compared to placebo (2.34 +/- .22 vs 1.87 +/- .10; mean +/- SE; p less than 0.05) as was log PD30 FEF25-75 (2.30 +/- .16 vs 1.72 +/- .08; p less than 0.005). These results indicate that cromolyn interferes with cholinergic induced bronchoconstriction and support the suggestion that it has an effect at a more fundamental level than the inhibition of antigen induced mediator release from mast cells.