Combinations of inhaled glucocorticoids and long-acting beta2-agonists in the same inhaler device have become available in recent years. In this double-blind, randomized, placebo-controlled and crossover study we have evaluated the onset of action of budesonide and formoterol in a single inhaler (Symbicort Turbuhaler) and that of the fixed combination of salmeterol and fluticasone (Seretide Diskus). Thirty patients with a mean FEV1 of 2.54 l (range: 1.48-4.28) and a mean inclusion reversibility in FEV1 of 19.1% were included. Single doses of budesonide/formoterol 160/4.5 microg and 2x (160/4.5) microg, salmeterol/fluticasone 50/250 microg, or placebo were given. Serial measurements of FEV1 were performed over 3 h. The combination of one or two inhalations of budesonide/formoterol showed a faster onset of action than salmeterol/fluticasone, both evaluated as mean FEV1 at 3 min (2.74, 2.75 and 2.56 l respectively P<0.001 for both doses of budesonide/formoterol), or as average FEV1 from 0 to 15 min (2.80, 2.83 and 2.67 l respectively P<0.001 for both doses of budesonide/formoterol). For placebo, mean FEV1 at 3 min was 2.46 l, and the average FEV1 at 0-15 min was 2.50 l. Furthermore, budesonide/formoterol at both doses resulted in higher FEV1 than salmeterol/fluticasone at 3 h. We conclude that the combination of budesonide/formoterol has a faster onset of action than salmeterol/fluticasone.