Pharmacoeconomic analysis involves the measurement of a ratio determining the extra costs required to achieve an additional unit of clinical benefit. Various techniques including modeling studies, retrospective analysis of databases, "piggy-back" economic analysis of prospective randomized clinical trials, and prospective randomized pharmacoeconomic trials have been developed to aid in economic and health decisions. In acute exacerbations of chronic obstructive pulmonary disease, it is possible to identify a group of patients that are at high risk of treatment failure from routine antimicrobial therapy, hospitalization, respiratory failure, and death. The cost of therapy for this relatively small group of patients is extraordinarily high. Data from a variety of approaches have suggested that aggressive antimicrobial therapy may lead to improved outcomes in these patients. The corollary is that aggressive therapy directed toward patients with either acute bronchitis (mainly a viral infection) or exacerbations of trivial chronic obstructive lung disease leads to emergence of resistance and increased costs.