These guidelines revise and replace United States Environmental Protection Agency (EPA) Guidelines for Carcinogen Risk Assessment published in 51 FR 33992, September 24, 1986. The guidelines provide EPA staff and decision makers with guidance for developing and using risk assessments. They also provide basic information to the public about the Agency's risk assessment methods. These guidelines are used with other risk assessment guidelines that the Agency has developed, such as the Mutagenicity Risk Assessment Guidelines (U.S. EPA, 1986c) and the Exposure Assessment Guidelines (U.S. EPA, 1992a). The guidelines encourage both regularity in procedures to support consistency in scientific components of Agency decision making and innovation to remain up-to-date in scientific thinking. In balancing these goals, the Agency relies on established scientific peer review processes (EPA, 27 1998b). The guidelines incorporate basic principles and science policies based on evaluation of the currently available information. As more is discovered about carcinogenesis, the need will arise to make appropriate changes in risk assessment guidance. The Agency will revise these guidelines when extensive changes are due. In the interim, the Agency will issue special reports, after appropriate peer review, to supplement and update guidance on single topics, (e.g., U.S. EPA, 1991b). The incorporation of new, peer-reviewed scientific understanding and data in an assessment is always consistent with the purposes of these guidelines.