The workshop was the outgrowth of a collaborative venture of the Committee on Response Strategies to Unusual Chemical Hazards and a counterpart Italian Committee to investigate the effects of area-wide chemical contamination at Seveso, Italy. The workshop served as a conceptual framework for the development and refinement of investigative approaches to the study and prediction of the health impacts of multichemical exposures. The workshop attempted to elucidate the analytic, environmental, and toxicologic problems associated with chemical mixtures, to describe state-of-the-art investigational procedures, and to advance concepts and approaches for the understanding of multichemical interactions influencing chronic risks to human health. This volume contains the papers that served as a basis for discussions at that conference. The papers are grouped into three major categories: Identification of Analytic Issues, Environmental Interactions, and Toxicological Interactions of Mixtures in Humans and Laboratory Animals.