On August 24-25, August 26-27, and September 9-10, 2004, the FIFRA Scientific Advisory Panel (SAP) will hold three separate meetings to consider and review three fumigant bystander exposure models. At the August 24-25 meeting the SAP will review the Probabilistic Exposure and Risk model for FUMigants (PERFUM) using iodomethane as a case study. On August 26-27, the SAP will review the Fumigant Exposure Modeling System (FEMS) using metam sodium as a case study. On September 9-10, the SAP will review the SOil Fumigant Exposure Assessment system (SOFEA(copyright)) using telone as a case study. In preparing for these meeting, preparation of this document, and development of questions for the Panel, the Agency has worked closely with scientists from the California Department of Pesticide Regulation who have significant experience with inhalation exposure modeling. The purpose of this document is to provide general background information for the FIFRA Science Advisory Panel (SAP) meeting pertaining to the evaluation of the Probabilistic Exposure And Risk Model For Fumigants (or PERFUM). PERFUM represents a potential evolution of the Agency's current methodology for calculating exposures to bystanders who can be exposed by being in close proximity to fields treated with soil fumigants prior to planting crops such as strawberries or tomatoes.