Indoor air pollution poses many challenges to the health professional. This booklet offers an overview of those challenges, focusing on acute conditions, with patterns that point to particular agents and suggestions for appropriate remedial action. The individual presenting with environmentally associated symptoms is apt to have been exposed to airborne substances originating not outdoors, but indoors. Studies from the United States and Europe show that persons in industrialized nations spend more than 90 percent of their time indoors. For infants, the elderly, persons with chronic diseases, and most urban residents of any age, the proportion is probably higher. In addition, the concentrations of many pollutants indoors exceed those outdoors. The locations of highest concern are those involving prolonged, continuing exposure--that is, the home, school, and workplace.