The Integrated Risk Information System (IRIS), an on-line database of chemical-specific risk information, was made available outside EPA. IRIS provides information on how chemicals affect human health and is a primary source of EPA risk assessment information on chemicals of environmental concern. 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; 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. Reference doses are estimated human chemical exposures over a lifetime which are just below the expected threshold for adverse health effects. Because exposure assessment pertains to exposure at a particular place, IRIS cannot provide situational information on exposure. IRIS can be used with an exposure assessment to characterize the risk of chemical exposure. This risk characterization can be used to decide what must be done to protect human health. Oral reference doses (RfD) are provided for most of the chemicals in IRIS and carcinogen slope factors are provided for some. Inhalation reference doses are not yet available in IRIS. Inhalation reference doses will be added after the Agency produces a methodology for developing these RfDs. For more information on IRIS call IRIS User Support at (513) 569-7254 or FTS 684-7254.