A total of 261 patients with symptomatic, mild to moderate asthma were randomized to treatment in this 4-week, double-blind, parallel-group comparison of fluticasone propionate 200 micrograms/d with beclomethasone dipropionate 400 micrograms/d. Improvements from both treatments were seen in diary card data. Morning peak expiratory flow rate (PEFR) improved from 375 to 390 and 371 to 382 l/min with fluticasone propionate and beclomethasone dipropionate, respectively. Symptom scores, percentage of symptom-free days and nights, and use of rescue beta 2-agonist medication also improved, as did clinical lung function. With the exception of percentage of rescue-free days, which was greater for beclomethasone dipropionate, none of the differences between the groups were statistically significant. There was a significant difference between treatments in the number of rescue-free days over days 1-28; however, there was no difference between treatments in the number of rescue-free days over days 1-14, nor was there any difference in the number of inhalations of rescue medication used throughout the study. Very few adverse effects were reported. Although all mean plasma cortisol values were within the normal range, they were significantly different between treatments, rising from 402 to 429 nmol/l with fluticasone propionate, and falling from 435 to 394 nmol/l with beclomethasone dipropionate (P = 0.006). Mean stimulated cortisol levels 30 min after tetracosactin injection were also significantly greater with fluticasone propionate (P = 0.024). In conclusion, fluticasone propionate 200 micrograms/d is as effective as beclomethasone dipropionate 400 micrograms/d with less effect on plasma cortisol levels.