Two multicenter, randomized, double-masked, placebo-controlled studies involving 451 adolescent and adult patients with mild-to-moderate asthma compared the efficacy and safety of salmeterol powder 50 micrograms twice daily with albuterol 180 micrograms four times daily or placebo (with albuterol as needed) for 12 weeks. Patients had forced expiratory volume in 1 second (FEV1) of 50% to 80%. Throughout the 12-week treatment period, the mean change from baseline in percentage of predicted FEV1 was significantly greater with salmeterol than with placebo; mean area under the curve for FEV1 was significantly greater with salmeterol than with albuterol or placebo. Significant improvements in morning and evening peak expiratory flow, percentage of nights without awakening, and asthma symptoms were observed with salmeterol. Salmeterol was well tolerated, and no clinically significant changes in electrocardiographic activity were observed.