The effect of nedocromil sodium on adenosine-induced bronchospasm was investigated in eight asthmatic patients. Nedocromil sodium (4 mg) administered by aerosol 10 min before challenge, effectively inhibited adenosine-induced bronchospasm. In another group of six asthmatic patients, nedocromil sodium administered in the same way did not reduce the bronchial response to methacholine. These results support the view that adenosine-induced bronchospasm may be prevented by a membrane stabilizing drug and is not mediated through cholinergic pathways. The mechanism(s) by which nedocromil sodium inhibits adenosine-induced bronchospasm requires further investigations.