This study evaluated the dose-response of the new long-acting muscarinic antagonist umeclidinium (GSK573719) in patients with COPD.This randomized, double-blind, placebo-controlled, parallel-group study evaluated three once-daily doses of umeclidinium (125, 250 and 500 μg) for 28 days in 285 patients with COPD having FEV(1) of 35-70% predicted (mean (SD) age=61.4 (8.41); mean (SD) post-bronchodilator FEV(1)=1.577 (0.450)). The primary endpoint was morning trough FEV(1) at Day 29. Secondary endpoints included 0-6h weighted mean FEV(1) and serial FEV(1) measured over 6h post-dose and at trough. Safety and pharmacokinetics were also assessed.All doses of umeclidinium significantly increased trough FEV(1) over placebo from 150 to 168 mL (p<0.001), 0-6h weighted mean FEV(1) from 113 to 211 mL (p<0.001), and serial FEV(1) at each point in time over 24h. Reductions in salbutamol use and improvements in FVC were noted for all doses. Umeclidinium was well tolerated with no apparent treatment-related changes in vital signs.Once-daily umeclidinium provides clinically significant, sustained improvement in lung function and is well tolerated.