Objectives: To determine the effect of adding salmeterol 50 μg twice daily for six months to current treatment in subjects with asthma who control their inhaled corticosteroid dose according to a management plan. Design: A double blind, randomised crossover study. Setting: Nottingham. Subjects: 101 subjects with mild or moderate asthma taking at least 200 μg twice daily of beclomethasone dipropionate or budesonide. Interventions: Salmeterol 50 μg twice daily and placebo for six months each, with a one month washout. Subjects adjusted inhaled steroid dose according to guidelines. Main outcome measure: Reduction in inhaled steroid use, exacerbations of asthma, and use of oral steroids. Results: Data were available for 87 subjects. When compared with placebo salmeterol treatment was associated with a 17% reduction in inhaled steroid use (95% confidence interval 12% to 22%) with no significant difference in the number of subjects who had an exacerbation (placebo 25%, salmeterol 16%) or use of oral steroids. For secondary end points salmeterol treatment was associated with higher morning and evening peak expiratory flow and forced expiratory volume in one second; a reduction in symptoms, bronchodilator use, and airway responsiveness to methacholine; and no effect on serum potassium concentration, 24 hour heart rate, or the final forced expiratory volume in one second achieved during a salbutamol dose-response study. Conclusions: In subjects who adjusted their inhaled steroid treatment according to guidelines the addition of salmeterol 50 μg twice daily was associated with a reduction in inhaled steroid use and improved lung function and symptom control. One hundred and one subjects with mild or moderate asthma took salmeterol 50 μg and placebo for six months each in a crossover study Subjects adjusted their inhaled steroid dose according to a management plan based on peak flow recordings and symptoms The dose of inhaled steroids was reduced by 17% with salmeterol, with no change in exacerbations or use of oral steroids Despite the reduction in inhaled steroid dose, salmeterol was associated with bronchodilatation and a reduction in symptoms The efficacy of salmeterol was maintained over the six months