Long-term treatment with cromolyn sodium will reduce airway hyperresponsiveness in patients with bronchial asthma. Short-term use of cromolyn sodium (less than 6 weeks) is effective in preventing seasonal increases in allergen-induced hyperresponsiveness. Cromolyn sodium therapy for greater than 12 weeks appears to be beneficial in reducing baseline hyperresponsiveness. The effect of cromolyn sodium on bronchial hyperresponsiveness may result from its ability to stabilize mast cells. Other contributory properties of cromolyn sodium are reviewed.