Bacillus thuringiensis (Bt) is a naturally occurring soil bacterium that produces proteins active against certain insects. Beginning in the mid-1990s, crop plants expressing Bt genes were commercialized in the United States. Cry1Ab and Cry1F Bt corn are effective in controlling certain pests of corn (European corn borer, corn earworm and southwestern corn borer), and Cry1Ac Bt cotton is effective in controlling certain pests of cotton (tobacco budworm, cotton bollworm and pink bollworm). Beyond the economic benefits to growers, the use of Bt corn and Bt cotton result in less risk to human health and the environment than chemical alternatives.In 2001, the US Environmental Protection Agency (EPA; Washington, DC, USA) reassessed the four still registered, but expiring, Bt crops that had been accepted for agricultural use in the preceding six years (from 1995 to October 2001; Table 1). The Bt crop reassessment approvals included provisions to prevent gene flow from Bt cotton to weedy relatives, increase research data on potential environmental effects and strengthen insect resistance management.From this reassessment, the EPA has determined that Bt corn and Bt cotton do not pose unreasonable risks to human health or to the environment. In this article, we summarize the supporting data and conclusions of the EPA. The complete reassessment document 1 , Biopesticides Registration Action Document (BRAD)-Bacillus thuringiensis Plant-Incorporated Protectants, which describes in detail the reassessment process, along with extensive references, can be found on the EPA website at h t t p : / / w w w . e p a . g o v / p e s t i c i d e s / biopesticides/pips/bt_brad.htm. Federal oversight of Bt crops Consistent with the Coordinated Framework for Regulation of Biotechnology