1. We conducted a descriptive cross-sectional study of asthma therapy among young adults to assess to what extent the current guidelines for asthma therapy have been implemented. In particular, we examined the use of inhaled corticosteroids in heavy users of inhaled beta-adrenoceptor agonists. 2. Data were retrieved from a population-based prescription database. For each of the years 1991 and 1994, all 20 to 44-year-olds who redeemed anti-asthma medication in the Odense area (210,000 inhabitants) were studied. 3. We identified the number of users and total sales volume for specific anti-asthma medications in defined daily doses (DDD) as well as the number of users and median annual doses of common regimens. Combined use of inhaled corticosteroids and inhaled beta-adrenoceptor agonists was also described. 4. The annual sales volume of anti-asthma drugs increased by 23% to 927,636 DDD from 1991 to 1994. Inhaled corticosteroids were mainly responsible for this with a 52% increase in number of users and an 88% increase in DDD. Inhaled beta-adrenoceptor agonists used in monotherapy remained the most popular regimen in 1994 (1685 users = 39%). Inhaled corticosteroids in combination with inhaled beta-adrenoceptor agonist were the second most popular regimen in 1994 (1308 users = 30%), increasing by 64% as compared with 1991. However, among patients with an annual use of inhaled beta-adrenoceptor agonist of 200 DDD (1600 "puffs') or more the percent of patients not receiving inhaled corticosteroids at all only fell from 37 to 33%. Though the number of patients being treated with inhaled corticosteroids has increased, there is still evidence of a substantial underuse.