The Department of the Interior's (Interior) U.S. Fish and Wildlife Service (Service) is generally required to use the best available scientific information when making key decisions under the Endangered Species Act (ESA). Controversy has surrounded whether former Deputy Assistant Secretary Julie MacDonald may have inappropriately influenced ESA decisions by basing decisions on political factors rather than scientific data. Interior directed the Service to review ESA decisions to determine which decisions may have been unduly influenced. ESA actions include, among others, 90-day petition findings, 12-month listing or delisting findings, and recovery planning. The Service distributed informal guidance in May 2005 on the processing of 90-day petitions. Recovery plans generally must include recovery criteria that, when met, would result in the species being delisted. GAO examined three separate issues: (1) what types of decisions, if any, were excluded from the Service's review of decisions that may have been inappropriately influenced; (2) to what extent the Service's May 2005 informal guidance affected 90-day petition findings; and (3) to what extent the Service has, before delisting species, met recovery criteria. GAO interviewed Service staff, surveyed Service biologists, and reviewed delisting rules and recovery plans. Interior did not provide comments in time for them to be included in this testimony.