This randomized, double-blind, parallel, multi-center study was designed to determine whether the addition of salmeterol to existing inhaled corticosteroid therapy provides greater therapeutic benefit than doubling the dose of inhaled corticosteroids in symptomatic patients with asthma. A total of 514 adults were randomized to either beclomethasone 168 micrograms plus salmeterol 42 micrograms twice daily or beclomethasone 336 micrograms twice daily for 24 weeks. Both treatments resulted in significantly improved symptom control and increased pulmonary function. However, beclomethasone plus salmeterol provided greater improvements than doubling the dose of beclomethasone (p < or = 0.05) in FEV1 and in daily-recorded measurements of morning (38 L/minute versus 20 L/minute after treatment with higher dose beclomethasone) and evening peak expiratory flow, asthma symptom scores, symptom-free days, supplemental albuterol use, and days and nights not requiring albuterol. There were no significant differences between treatment groups in the number of patients with abnormal response to corticotropin stimulation at Treatment Week 24. No treatment differences in asthma exacerbation and adverse event frequency rates were seen. Beclomethasone 168 micrograms plus salmeterol 42 micrograms administered twice daily was superior to beclomethasone 336 micrograms taken twice daily in patients symptomatic on beclomethasone 168 micrograms, with no added safety risks.