This workshop was an undertaking of the Committee on Response Strategies to Unusual Chemical Hazards and its counterpart Italian Committee. The Committee was established in 1979 as a result of the 1976 chemical explosion in Seveso, Italy to develop guidelines that might be used to implement a world-wide mechanism for guiding biomedical researchers at the scene of accidents similar to that at Seveso, and to evaluate newer health data from the Seveso accident and the design of future studies. The topic of the workshop, Plans for clinical and epidemiologic follow-up after area-wide chemical contamination, was approached from two points of view: first, by exploring a number of cases in which such widespread contamination occurred and which served as the basis for field studies; and second, by evaluating diseases and target organs that were identified as likely outcomes of chemical exposures. A synthesis of experiences and guiding principles for future investigations of similar exposures was provided by a panel of experts from the U.S. and Italy.