The magnitude and duration of the inhibitory effect of three doses of cromolyn sodium on the airway response to hyperventilation of cold dry air was examined in a double-blind, randomized controlled trial. Eight subjects with well controlled asthma were studied. On 4 separate days, doses of either 2 mg, 10 mg, 20 mg, or placebo were administered by metered-dose inhaler. Twenty minutes, 2 hours, and 4 hours after each medication, airway responsiveness to isocapnic hyperventilation of cold dry air was measured by use of a standardized dose-response method. At 20 minutes, all three doses inhibited bronchoconstriction, and there was no evidence of any difference in the magnitude of the inhibition between the doses. All three doses progressively provided less protection with time. By 2 hours, the inhibition induced by 2 mg was no longer different from placebo, and by 4 hours, only 20 mg still provided significant protection. The results demonstrate that, although the initial magnitude of inhibition may not be different between 2 mg and 20 mg, the rate at which the protective effect wears off is dose related.