It has been suggested that the new long-acting beta 2-agonist, salmeterol, has anti-inflammatory properties--properties which should improve airway responsiveness (AR). Conversely, several recent studies have suggested that regular beta 2-agonist treatment may worsen asthma and AR. Furthermore, a short-lived rebound increase in AR has been described following cessation of regular treatment with these agents. We have consequently assessed the effects on AR of regular treatment with either salmeterol or salbutamol at conventional doses over 6 weeks. FEV1 and AR were measured five times in 20 asthmatic subjects randomly allocated to one or other treatment regimen; twice during a 2-week run-in period; and 24 h, 72 h, and 2 weeks after the last dose of the study medication. Peak expiratory flow rate (PEFR) was also recorded throughout the study period. There were no statistically significant changes in FEV1 or AR between the run-in period and any of the post treatment measurements for either of the treatments used. Mean PEFR was significantly higher during the treatment period than the run-in period for the salmeterol group, but not the salbutamol group, confirming that therapeutically adequate doses of salmeterol had been given. We conclude that if the regular use of salmeterol is associated with beneficial or adverse effects on AR, this is not apparent after a treatment period of 6 weeks.