Copyright ©ERS Journals Ltd 1998 European Respiratory Journal

Inhaled β2-agonists are the most effective bronchodila-tors in current use and are the most widely prescribed sym-ptomatic antiasthma therapy in the world. The introduction of long-acting inhaled β2-agonists, formoterol and salme-terol, has been an important advance in asthma therapy. Current guidelines recommend that short-acting β2-ago-nists should be used only as relief medication, whereas long-acting β2-agonists should be introduced for regular use in patients with asthma already receiving inhaled ster-oid therapy [1]. The clinical efficacy and long duration of action of for-moterol and salmeterol appears to be very similar [2–4] despite the fact that salmeterol has a longer duration of action than formoterol in vitro [3, 5]. There are, however, some interesting differences between the two compounds