This document is the final report for the 2004 external peer review of the Proposed Oral Reference Dose (RfD) for Barium and Compounds, prepared by the U.S. Environmental Protection Agency (EPA), National Center for Environmental Assessment (NCEA), for the Integrated Risk Information System (IRIS). A panel of external peer reviewers met to discuss their responses to the charge questions on June 10, 2004. A supplemental teleconference was held on July 21, 2004, to ensure that reviewers had the opportunity to review and discuss public comments that had been submitted to EPA before they finalized their comments. This document contains the final written comments of the external peer reviewers.