Sick building syndrome embodied a politics of uncertainty that continues to characterize contemporary American environmental debates. Michelle Murphy explores the production of uncertainty by juxtaposing multiple histories, each of which explains how an expert or lay tradition made chemical exposures perceptible or imperceptible, existent or nonexistent. She shows how uncertainty emerged from a complex confluence of feminist activism, office worker protests, ventilation engineering, toxicology, popular epidemiology, corporate science, and ecology. In an illuminating case study, she reflects on EPA scientists' efforts to have their headquarters recognized as a sick building. Murphy brings all of these histories together in what is not only a thorough account of an environmental health problem but also a much deeper exploration of the relationship between history, materiality, and uncertainty.