Environmental exposure assessment, an intermediate step in risk analysis, ties projected volumes of toxic materials entering the environment to specific environmental effects. Thus, prediction of the environmental fate and distribution of a toxic compound is an integral part of any hierarchical scheme of risk analysis. Environmental exposure assessment is a new and emerging science, and although some processes have not been adequately characterized, tests for the most significant ones are available. Both screening tests and detailed protocols are presently available for determining the process kinetics for selected chemicals exposed to differing environmental conditions. The greatest unrealized potential for exposure assessment lies in the use of mathematical models. When environmental exposure models are coupled with environmental effects models, powerful tools for risk assessment emerge. Such sophisticated models need to be refined and verified, however, before risk analysis becomes accurate and cost-effective.