Fourteen adult subjects with stable asthma were treated using a double-blind crossover, randomised protocol, with either nedocromil sodium (4 mg or 2 mg) or placebo. The agents were administered from matched pressurised aerosol inhalers 30 min before exposure to an exercise regimen which, on a previous screening day, resulted in a 24-53% (mean: 33.9%) decrease in peak expiratory flow (PEF). Both doses of nedocromil sodium were significantly superior to placebo in preventing the exercise-induced decrease in PEF and were without side effects. This study confirms and extends the results of earlier trials with nedocromil sodium and further supports the contention that this new agent may be of benefit in the treatment of reversible obstructive airways disease in the adult patient.