Three hundred forty-nine patients with asthma previously treated with medium doses of inhaled corticosteroids during a 2-wk, single-blind, run-in period were randomized to treatment with salmeterol 50 microg combined with fluticasone propionate (FP) 250 microg, salmeterol 50 microg, FP 250 microg, or placebo, each given twice daily through a Diskus device for 12 wk. Mean change in FEV(1) at endpoint was significantly (p </= 0.001) greater with the salmeterol/FP combination product (0.48 L) than with placebo (-0.11 L), salmeterol (0.05 L), or FP (0.25 L). The combination product significantly increased the area under the 12-h serial FEV(1) curve relative to baseline over that with placebo, salmeterol, or FP at Day 1, Week 1, and Week 12 (p </= 0.025). Patients in the combination-product group had a significantly greater probability of remaining in the study without being withdrawn because of worsening asthma than did patients in the placebo, salmeterol, or FP groups (p </= 0.002). The combination product significantly increased (p < 0. 001) morning PEF at endpoint (53.5 L/min) as compared with placebo (-14 L/min), salmeterol (-11.6 L/min), or FP (15.2 L/min). The combination product significantly (p </= 0.011) reduced asthma symptom scores and supplemental albuterol use, and significantly increased the percentage of nights with no awakenings as compared with placebo, salmeterol, and FP (p </= 0.016). Combination treatment with salmeterol 50 microg and FP 250 microg given twice daily from the Diskus device provided better asthma control and greater improvement in pulmonary function than did the individual agents, and may simplify the management of asthma in patients who need both classes of drugs for optimal control of their disease.