In 2005, the American Thoracic Society marks its 100th year of existence. For over a third of this span, since 1967, clinicians and investigators have struggled with a common, often lethal condition originally termed the adult respiratory distress syndrome (ARDS)(1).* While the syndrome almost certainly occurred in earlier times well before the advent of intensive care units, this date establishes its modern era. Subsequently, ARDS has more correctly come to indicate the acute respiratory distress syndrome because it occurs in children as well as in adults (2). ARDS causes severe acute respiratory failure with dynamic impairment in oxygen and carbon dioxide transfer, with the need for high levels of supplementary oxygen and a high minute ventilation (3, 4). Efforts to understand the pathophysiologic events underlying ARDS, a constellation that is now generally termed acute lung injury (ALI), have been substantial and remain a priority of the National Institutes of Health (5). The expectation has been that basic, translational, and clinical studies will result in new strategies for management of ALI/ARDS based on clear definition of the cellular and molecular events requisite in lung injury and repair. While important discoveries have been made, the goal of fundamental characterization of ALI/ARDS in a way that results in highly effective prevention and treatment remains incomplete and elusive. One major advance in supportive care, a strategy of lung protective mechanical ventilation, has substantially reduced mortality in ALI/ARDS (6, 7). This therapeutic intervention resulted from both experimental and clinical studies that evaluated the effect of different ventilation strategies on the course of ALI, and continues a theme initiated in the original description of ALI/ARDS in which positive end-expiratory pressure was introduced as a management modality (1). In spite of the advances in supportive care of patients with