Pursuant to a congressional request, GAO examined the conduct and findings of the Air Force's Ranch Hand study on the long-term health effects of exposure to herbicides, such as Agent Orange, in Vietnam, and assessed the study's impact on determinations of veterans' compensation, focusing on: (1) whether the study's findings and data have been properly and promptly reported and disseminated; (2) the statistical limitations of the study and whether they have been adequately reported and communicated; (3) the measures established to monitor the study's conduct and to prevent improper influence, particularly those involving the Ranch Hand Study's Advisory Committee; and (4) the impact of the study on determinations of diseases for which Vietnam veterans are eligible to receive compensation benefits.