This document is a statement of the quality assurance (QA) policy of the Health Effects Research Laboratory (HERL), US Environmental Protection Agency, Research Triangle Park, North Carolina. It describes the HERL QA organization and the QA responsibilities of both management and technical research personnel in relation to the mandatory Agency QA policy and project data quality requirements. It provides guidelines for managers in the implementation of Agency QA policy and evaluation of research documentation, and presents guidelines for project officers for 1) specification of QA requirements for extramural and intramural tasks, 2) preparation of QA project plans and research protocols for intramural research and support tasks, 3) review and evaluation of QA program and project plans for extramural projects, and 4) review and evaluation of data quality throughout the project term. Aspects of research projects that must be considered by project officers in the development or review of QA plans are treated in detail. These guidelines are reviewed and revised annually by the HERL QA office, the QA committee, and HERL division directors.