Sixteen patients suffering from bronchial asthma, with or without chronic bronchitis, sufficiently severe to be treated with inhaled corticosteroids, were studied in a single-blind trial (blind observer) of beclomethasone dipropionate (BDP) given in three randomized dosage regimens: 500, 1000 and 2000 micrograms per day, each for 4 weeks. The beta 2-adrenergic agonist response curve showed a dose-dependent increase in FEV1 which was not affected by different doses of BDP. A small but significant reduction in basal cortisol levels was observed after BDP 500 micrograms/day. There was no significant difference between the various doses of BDP in reducing cortisol level and stimulation with tetracosactide remained unchanged. The study showed a gradual, dose-dependent improvement in lung function, statistically significant for morning peak expiratory flow rate at BDP 2000 micrograms/day. Dyspnoea score and beta 2-agonist use decreased, reflecting the anti-asthmatic effects. An increase in total leukocyte count was observed, together with a decrease in the eosinophil count. Oral candidiasis was seen in 2 out of 16 patients. It is concluded that the clinical anti-asthmatic effects of corticosteroid treatment by inhalation are not due to modulation of beta 2-receptor function in the airways.