For subjects with EIA participating in physical activities throughout the day, prolonged duration of protection is desirable. The purpose of this study was to determine whether in EIA a combination of the recommended aerosol doses of the beta 2-adrenergic receptor agonist, terbutaline sulfate (0.5 mg), and cromolyn sodium (disodium cromoglycate; 2 mg) provides longer protection against EIA than either drug alone. On four separate days, following the administration of either placebo, terbutaline alone, cromolyn sodium alone or terbutaline and cromolyn sodium together, 12 subjects (seven men and five women; aged 18 to 28 years) with EIA performed four identical eight minute treadmill runs, each separated by two-hour intervals. Drug treatments were given double-blind, with the order counterbalanced using a Latin-square design. Pulmonary function was recorded before the drug, immediately before and after exercise, and at 3, 4, 5, 6, 7, 10, 15, and 30 minutes after exercise. Inspired ventilation, heart rate, and environmental conditions were monitored during exercise. A two-way analysis of variance was performed to investigate the main effects of time and drug treatment. Results indicated that in comparison with placebo, EIA was significantly reduced by either cromolyn sodium or terbutaline administered up to two hours (p less than 0.01) and by the combination (cromolyn sodium and terbutaline) up to four hours after inhalation (p less than 0.05). No significant differences were found between the combination and terbutaline during the initial two hours (p less than 0.5). We conclude that a combination of beta 2-adrenergic receptor agonist and cromolyn sodium is the treatment of choice for prolonged effective protection from EIA.