Risk assessment of mixtures of environmental pollutants has become a subject of increasing public and regulatory concern. Typically, assessment of mixtures has been based on aggregating the risks associated with the individual constituents of the mixture. This approach does not consider the potential synergistic and antagonistic effects of the components, and does not incorporate the risk associated with unidentified constituents or constituents for which the individual risks are not known. On June 7-9, 1988 the U.S. Environmental Protection Agency (EPA) held an 'International Symposium on Chemical Mixtures: Risk Assessment and Management' in Cincinnati, OH, to provide a forum where critical issues concerning assessment of mixtures could be presented and discussed. Approximately 200 scientists attended, representing a wide variety of disciplines, institutions, and countries. During the two-and-one-half days of the symposium, leaders in the multidisciplinary field of risk assessment presented state-of-the-art approaches and techniques for quantifying the potential health risks from exposure to chemical mixtures. They also addressed current knowledge in the various disciplines of risk assessment, as well as recent developments in sources of exposure, pharmacology, and toxicology. The symposium was dedicated to the memory of Dr. Jerry Strata, founder and director of the EPA Environmental Criteria and Assessment Office.