The aims were to determine the effect of an oral inhibitor of the signaling mediator p38 mitogen-activated protein kinase (GW856553, losmapimod) on sputum neutrophils, pulmonary function, and blood biomarkers of inflammation in chronic obstructive pulmonary disease (COPD). Three hundred and two individuals with GOLD stage II COPD were randomized to oral losmapimod 7.5 mg twice daily, inhaled salmeterol/fluticasone propionate 50 μg/500 μg combination (SFC), or placebo in a 12-week, randomized, double-blind, double-dummy study (MKI102428/NCT00642148). Neither losmapimod nor SFC had an effect on the primary end point of sputum neutrophils. Losmapimod was well tolerated and reduced plasma fibrinogen by 11% (-0.4 g/L, ratio of effect of losmapimod/placebo 0.89; 95% confidence interval, 0.83-0.96; P = .002) with nonsignificant reductions in interleukin-6, interleukin-8, and C-reactive protein. There was evidence of improvement in hyperinflation with losmapimod compared with placebo (overall P = .02). Inhaled SFC significantly improved lung function and reduced serum CC-16 (ratio of effect of SFC/placebo 0.87; 95% confidence interval, 0.82-0.93; P < .001). It was concluded that oral losmapimod significantly reduced plasma fibrinogen in patients with COPD.