Seventeen children with asthma were studied in a double-blind, crossover, placebo-controlled study designed to compare the efficacy of cromolyn sodium with that of nedocromil sodium in preventing exercise-induced asthma. All drugs were delivered through a metered-dose inhaler (cromolyn sodium, 10 mg; nedocromil sodium, 4 mg; placebo, two puffs). Nedocromil sodium and cromolyn sodium provided significant, comparable protection from exercise-induced asthma, and both drugs were better than placebo. We conclude that nedocromil sodium and cromolyn sodium administered by a pressurized aerosol provide equal protection against exercise-induced asthma in children.