Chronic obstructive pulmonary disease (COPD) is a common condition, and one difficult to manage. Available treatments, other than smoking cessation, are only minimally effective, and the knowledge basis for clinical decision making is limited. To identify areas in which further clinical research may lead to significant improvements in the care of patients with COPD, the National Heart, Lung, and Blood Institute convened a Working Group, entitled "Clinical Research in COPD: Needs and Opportunities," on March 21-22, 2002. This group of experts identified important questions in the field and made the following recommendations: (1) establish a multicenter Clinical Research Network to perform multiple, short-term clinical trials of treatments in patients with moderate-to-severe COPD; (2) create a system for the standardized collection, processing, and distribution of lung tissue specimens and associated clinical and laboratory data; (3) develop standards for the classification and staging of COPD; (4) characterize the development and progression of COPD using measures and biomarkers that relate to current concepts of pathogenesis; and (5) evaluate indications for long-term oxygen therapy for patients with COPD.