Inhaled beta2-agonists have been subject to restrictions in relationship to sports due to fear of possible improvement in endurance performance. According to the international doping regulations only inhaled salbutamol, terbutaline and salmeterol are allowed for use in sports. Formoterol is a recently introduced rapid onset-long-acting inhaled beta2-agonist. The main aim of the present randomized, double-blind placebo-controlled study was to investigate possible improvement in endurance performance of inhaled formoterol in 24 healthy well-trained competitive male athletes, 21-29 years old. Lung function (flow-volume loops) was measured before, 15 min after each inhaled study drug and before and repeatedly after exercise. On day 1, maximum oxygen uptake (VO2max), peak ventilation (VEpeak) and running time till exhaustion were measured and used to determine the exercise load on days 2 and 3. On days 2 and 3 the subjects inhaled the study drugs, rested for 1 h, then exercised, and VO2max, VEpeak and running time until exhaustion were determined. Inhaled formoterol did not improve any parameter of endurance performance. On the other hand a statistically significant, although not clinically significant (0.05 ml(-1) min kg(-1)), change was found in estimated difference of VO2max between formoterol and placebo in favour of placebo. Lung function increased significantly after inhaled formoterol, and after exercise also for placebo, but without differences between the beta2-agonist and placebo after exercise. In conclusion, inhaled formoterol did not improve endurance performance compared to placebo.