We compared the effects of salmeterol (Sm) (50 micrograms twice daily) with that of salbutamol (Sb) (200 micrograms four times daily) and placebo (P) in patients with mild-to-moderate asthma with asthma symptoms and related the effectiveness of these therapies between patients who used concurrent inhaled corticosteroids (ICS) and those who did not. The study was a 12-wk, multicenter, double-blind, placebo-controlled crossover trial with 367 adult asthmatics randomized to each trial medication for 4 wk. Inhaled Sb was provided as rescue medication to all patients throughout the trial. Only 80% of patients, albeit the majority, were receiving maintenance treatment with ICS throughout this trial; this reflects practice current in early 1990. Each study day, patients recorded their morning and evening peak expiratory flows (PEF), assessment of asthma symptoms, and use of rescue medication. Both morning and evening PEF were greater during treatment with Sm than with Sb (mean differences between the treatments of 29.8 and 14.3 L/min, respectively) or P (27.7 and 20.3 L/min, respectively) (p < 0.0001). Sm was also more effective than Sb or P in lowering diurnal variation in PEF and increasing the percentage of symptom-free days and rescue-free days and nights with no sleep disturbance (p < or = 0.0004). Sb was more effective than P in increasing evening PEF and the percentage of symptom-free days (p < 0.05) and rescue-free days (p < 0.0001). The same clinical superiority of Sm compared with Sb and P was observed in those patients using ICS (p < 0.001 for all treatment comparisons), and to a greater extent than in those patients not using ICS (i.e., Sm was more effective than Sb and P in just six of the 20 treatment comparisons; p < 0.05). In conclusion, Sm 50 micrograms twice daily is effective in the management of mild-to-moderate asthma and it further improves asthma control in patients already using ICS.