This double-blind, randomised, placebo-controlled crossover trial in 18 adults with asthma evaluated the onset of efficacy of doses of 12 and 24 micrograms eformoterol delivered as a dry powder, and compared patients' subjective assessments of efficacy with objective measures. Bronchodilatory efficacy was measured in terms of specific conductance (sGaw) and forced expiratory volume in one minute (FEV1). With both doses of eformoterol, a bronchodilatory effect was observed one minute after inhalation. The difference in bronchodilator effect (sGaw and FEV1) between both eformoterol doses and placebo was statistically significant (p < 0.01) from one minute onwards. No significant difference in onset of action or peak effect was seen between the two doses of eformoterol. Patients' subjective reports were closely related to the observed onset of efficacy and indicated no difference between the two eformoterol doses.