The accident on September 21, 2001, at the AZF factory in Toulouse resulted in the release of pollutants into the air, water, and soil both during and after the explosion. Assessing the health risks associated with this pollution was one of the three main areas of focus for the epidemiological surveillance program monitoring the health consequences of the disaster. Given the potentially incomplete identification of the released substances and the lack of environmental measurements for some of the identified substances (chlorine, nitric acid, nitrous oxide), two specific objectives were assigned to the study: - to characterize the risks associated with acute and subchronic exposure to the measured pollutants; - to detect, in the general population and in groups particularly exposed, the health effects—whether predictable or not—associated with exposure to identified or unidentified substances. (R.A.)