CalTOX is an innovative spreadsheet model that relates the concentration of an organic chemical in soil to the risk of an adverse health effect for a person living or working on or near the contaminated soil. It computes site-specific health-based soil clean-up concentrations given target risk levels or human health risks given soil concentrations at the site. The CalTOX spreadsheet contains a multimedia transport and transformation model that uses equations based on conservation of mass and chemical equilibrium. The model predicts the time-dependent concentrations of a chemical in the eight environmental compartments of air, surface water, groundwater, three soil layers, sediment, and plants at a site. After partitioning the concentration of the chemical to these environmental compartments, CalTOX determines the chemical concentration in the exposure media of breathing zone air, drinking water, food, and soil that people inhale, ingest and contact dermally. CalTOX then uses the equations found in the U.S. Environmental Protection Agency Risk Assessment Guidance for Superfund (US EPA RAGS) to estimate exposure and risk. CalTOX has the capability of conducting Monte Carlo simulations with a spreadsheet add-in program. Used in this way, CalTOX will present a range of risks or health-based soil target clean-up levels that reflect the uncertainty/variability of the estimates. The Science Advisory Board of the US Environmental Protection Agency has lauded CalTOX as 'potentially the most advanced of all the models ... with respect to exposure'. The Risk Assessment Advisory Committee convened by the California state legislature favorably reviewed CalTOX as a new tool that carries out 'risk assessment activities better than could be done with existing tools'. To obtain meaningful results, CalTOX users must have a solid understanding of the risk assessment including toxicology, environmental transport of chemicals, the RAGS process and probabilistic methods for estimating risk. Therefore, experience with EXCEL spreadsheets and telecommunications computer BBS is advisable. For additional information, call the NTIS Automatic Fax Service, dial (703) 487-4146, enter mailbox no. 700, and product code no. 9550.