The Guidelines for Estimating Exposure provided the general principles and a logical process to follow in evaluating exposure for risk assessment purposes. This past December the U.S. EPA published in the Federal Register proposed additional guidelines in the form of Exposure-Related Measurements. These proposed guidelines significantly expanded the concept of exposure assessment related to the 1986 guidelines. As part of the proposed guidelines, three general approaches to exposure assessment are discussed, namely predictive, reconstructive, and direct exposure assessments. Within these three approaches, the guidelines discuss the purpose of making exposure-related measurements, as well as using measurements in exposure assessments. In addition, the guidelines also propose a glossary of terms which describes or defines commonly used terms in exposure assessments.