The objective of this study was to investigate initial maintenance treatment with salmeterol/fluticasone propionate (Seretide) 50/250 microg twice daily (SFC) compared with fluticasone propionate (Flixotide) 250 microg twice daily (FP) (both via Diskus inhaler, GlaxoSmithKline, Greenford, UK) in patients with moderate persistent asthma currently only treated with inhaled short-acting beta2-agonists. A total of 362 adults and adolescents (12 to 80 years of age) were randomized to this 12-week double-blind parallel-group study. The primary endpoint was mean morning peak expiratory flow (PEF). Secondary efficacy endpoints included median percentages of symptom-free and rescue-free days and nights; the percentage of patients who achieved the pre-defined criteria for well-controlled asthma over weeks 5 to 12; and the incidence of asthma exacerbations. Safety was assessed by the incidence of adverse events. Superiority of SFC over FP alone was demonstrated for the primary and each secondary endpoint. The difference in adjusted mean change from baseline in morning PEF between SFC and FP was 21 L/min (95% CI: 11, 31; p<0.001). Significantly more patients achieved well-controlled asthma during treatment with SFC (46%) compared with FP (32%) (odds ratio 1.84; 95% CI: 1.17, 2.89; p=0.008). Both treatments were safe and well-tolerated. This study demonstrates that initial maintenance treatment with SFC 50/250 mug twice daily provides superior efficacy to FP 250 microg twice daily alone in patients with moderate persistent asthma.