This document describes the direction in which the Office of Research and Development (ORD) human health risk assessment research program is expected to evolve over the next several years. The ORD research planning process involves a series of steps designed to identify, verify, and document research priorities. This research strategy represents a step in this process; it is both an elaboration of the description of ORD's human health risk assessment research program contained in the ORD Strategic Plan and an outline for development of the more specific laboratory/center implementation plans. This document describes ORD's human health research program that addresses key uncertainties in human health risk assessment. This research strategy is an attempt to build consensus for a focused, integrated research agenda that will strengthen the scientific foundation for future risk assessments.