The label "sick building syndrome" is often used to imply the absence of a physiologic basis for symptoms in the built environment. Although building-related illness is widely recognized but considered rare, several well-studied mechanisms may be responsible for many symptoms in buildings. These mechanisms do not explain why some individuals perceive disability. Until researchers distinguish physiologic mechanisms from other aspects of disease and study them systematically, poorly defined symptoms will remain poorly understood. The disability associated with such symptoms and syndromes, not the physiology, is the primary interest and generates controversy.