To evaluate whether the potency of a long-acting selective beta 2-agonist negates the need for cromolyn, 27 children, aged 6 to 12 years, with mild to moderate asthma requiring long-term medication, were assessed for the therapeutic effects of cromolyn and/or terbutaline by jet nebulizer. Patients received either cromolyn, 20 mg, terbutaline, 0.1 mg/kg up to 4 mg, or the combination, three times daily. The study design was double-blind, crossover with each patient receiving the three treatment regimens in randomized order for a period of 8 weeks each. Daily diary mean scores generally demonstrated best symptom control with cromolyn or the combination than with terbutaline alone. Cough was significantly less with cromolyn than with terbutaline (p less than 0.05). Morning peak flow measures were higher with combination therapy than with terbutaline (p less than 0.05). Evening peak flow measures were higher with the combination and cromolyn alone than with terbutaline alone (p less than 0.01). Methacholine challenge demonstrated less bronchial hyperreactivity with the combination or cromolyn alone than with terbutaline alone (p less than 0.02). The effectiveness of the nebulizer regimen for children with chronic asthma is better when cromolyn is used alone or in combination with terbutaline than when the beta-agonist is used alone.