There is increasing evidence that chronic obstructive pulmonary disease (COPD) is associated with chronic inflammation in the airways and lung parenchyma; however, little is known about the inflammatory response during acute COPD exacerbation. The objectives of this study were (1) to determine if inflammatory markers associated with neutrophilic inflammation and activation increase at times of acute COPD exacerbation relative to the clinically stable state, and (2) to determine whether the presence of acute bacterial or viral infection at the time of COPD exacerbation could be correlated with increases in sputum markers of inflammation. Induced sputum was collected from patients with COPD when they were clinically stable, during the time of an acute exacerbation, and 1 mo later. Sputum was analyzed at each time point for soluble markers associated with neutrophilic inflammation; myeloperoxidase (MPO), tumor necrosis factor-alpha (TNF-alpha), and interleukin-8 (IL-8). Serologic assays on acute and convalescent sera were performed for respiratory viruses, and induced sputum was also subject to quantitative bacterial cultures, viral cultures, and polymerase chain reaction (PCR) for detection of respiratory viruses. Fourteen of the 50 patients enrolled in the study met predetermined criteria for an acute COPD exacerbation over the 15-mo study period. TNF-alpha and IL-8 were significantly elevated in the sputum of patients during acute COPD exacerbation compared with when they were clinically stable (p = 0.01 and p = 0.05, respectively). Concentrations of these cytokines declined significantly 1 mo after the exacerbation. Three of 14 patients (21%) had confirmed bacterial or viral respiratory tract infections. Patients with documented infection did not demonstrate greater increases in sputum levels of inflammatory cytokines during exacerbations compared with patients without demonstrable infection. We conclude that markers of airway neutrophilic inflammation increase at the time of acute COPD exacerbation and then decline 1 mo later, and that this acute inflammatory response appears to occur independently of a demonstrable viral or bacterial airway infection.