The Integrated Risk Information System (IRIS), an on-line database of chemical-specific risk information, provides information on how chemicals affect human health and is a primary source of EPA risk assessment information on chemicals of environmental concern. It is intended to serve as a guide for the hazard identification and dose-response assessment steps of EPA risk assessments. IRIS makes chemical-specific risk information readily available to those who must perform risk assessments and also increases consistency in risk management decisions. The principal section of IRIS is the chemical files. The chemical files contain: oral and inhalation reference doses for noncarcinogens; oral and inhalation carcinogen assessments; summarized Drinking Water Health Advisories; summaries of selected EPA regulations; and supplementary data (for example, acute toxicity information and physical-chemical properties). The two primary types of health assessment information in IRIS are reference doses and carcinogen assessments.