In this double blind study, 10 patients with bronchial asthma underwent exercise challenge on 5 occasions. The first of these was a control test carried out without prior drug administration; the other tests were preceded by the administration, in random order, of a sodium cromoglycate (SCG) capsule, a placebo capsule, an ampoule of sodium cromoglycate solution and a placebo ampoule. Comparisons of the largest falls in PEFR [peak expiratory flow rate] after exercise showed statistically significant inhibition of exercise-induced bronchospasm, compared with control, with both SCG inhalation solution (P < 0.01) and SCG powder (P < 0.01). SCG powder was more active, but the difference was not significant. A significant difference in protection was found between SCG powder and its placebo (P < 0.01). SCG inhalation solution was also more effective than its placebo, but the difference did not reach significance, since the latter conferred some protection.