As an initial investigation to determine whether or not inhaled corticosteroids can be discontinued, we evaluated the results of discontinuation in patients who had been well controlled with inhaled corticosteroids for more than one year prior to this study. The average dose of BDP which the patients had been inhaling at the start of this study was 365 micrograms/day. To determine the effect of discontinuing inhaled corticosteroids, we compared the patients' peak expiratory flow rates and the frequency of beta-agonist use between the 4-week observation period and follow-up periods of varying duration. Only three out of twenty patients enrolled were able to maintain their discontinuation of BDP, while the remaining seventeen patients restarted after a mean period of 30.8 days. Mean peak flow values began to fall during the first week after discontinuation, and decreased morning peak flow values became significant in the 2nd, 3rd and 4th weeks. The mean peak flow value during the observation period was 85.2% of each patient's personal best, but had dropped to 68.8% of this level just before restarting inhaled corticosteroid. The frequency of beta-agonist use during the study period (2.99 +/- 3.39 times a day) was significantly higher than during the observation period (1.94 +/- 2.95 times a day). This finding strongly suggests that the patients' asthmatic conditions had become unstable during the study period. These results suggest that any decision to discontinue the use of inhaled corticosteroid, even in well controlled patients with chronic asthma, should be taken with great care.