This article is a critical analysis of a study published in the journal *Inhal Toxicol*, 2000, 12 (Suppl 4):75-90. The objective of this study is to investigate an association between air pollution and hospital admissions for chronic obstructive pulmonary disease (COPD) in three geographic regions of the United States (Chicago, Los Angeles, and Phoenix). Unlike the studies reviewed by Dockery and Pope, this work shows that results vary by geographic area when examining particulate matter. Particulate matter is associated with hospital admissions for COPD only in Los Angeles. (Excerpts from the article).