This report discusses application of the benchmark dose (BMD) approach to human health risk assessment, specifically in the calculation of reference doses (RfDs) and reference concentrations (RfCs). An RfD or RfC is an estimate of daily exposure (RfD) or continuous inhalation exposure (RfC) to the human population (including sensitive subgroups) that is likely to be without appreciable risk of deleterious effects during a lifetime. EPA frequently uses RfDs and RfCs, along with other scientific information, in setting standards for noncancer human health effects. EPA believes that the BMD approach presents a significant opportunity to improve the scientific basis of noncancer risk assessment and overcome some of the limitations to the current alternative basis for calculating RfDs and RfCs, the NOAEL (no observed adverse effects level). This document aims to encourage further application and development of the method by outlining the benchmark approach.