Long-term effects of a long-acting beta2-adrenoceptor agonist, salmeterol, on airway hyperresponsiveness in patients with mild asthma - Cheung,D.; Timmers,M.C.; Zwinderman,A.H.; Bei,E.H.; Dijkman,J.H.; Sterk,P.J. (N Engl J Med, 1992)