Preclinical studies suggested that aclidinium and glycopyrronium might have a faster onset of action than tiotropium. In this study we assessed the onset of action of aclidinium and glycopyrronium versus tiotropium, all administered at the approved clinical doses, in patients with moderate-to-severe chronic obstructive pulmonary disease (COPD) and in human isolated bronchi by using different concentrations. Sixteen COPD patients inhaled single doses of aclidinium 400µg, glycopyrronium 50μg and tiotropium 18µg and FEV1 was measured to assess their onset of action. In human isolated bronchi the time to evoke half maximal relaxation of transmural stimulation was tested from 10nM to 1µM for each drug. Nine, eight and twelve patients did not achieve 15% increase of FEV1 after inhalation of aclidinium, glycopyrronium and tiotropium, respectively. Aclidinium (15.6±7.5min) and glycopyrronium (17.9±10.4min) enhanced 15% FEV1 more rapidly than tiotropium (42.5±19.4min), with no significant difference (P>0.05). In isolated airways, glycopyrronium elicited a dose-dependent onset of action (10nM: 8.2±1.3min, 100nM: 7.1±2.1min, 1μM: 3.4±0.4min) that was faster compared to that induced by aclidinium (1μM: 6.4±0.5min) and tiotropium (1μM: 8.4±1.1min) (P