In 1997, the EPA promulgated a final rule under section 5 of Toxic Substances and Control Act (TSCA) to establish the notification procedures for review of certain new microorganisms before they are introduced into commerce. ‘‘New' microorganisms are those formed by deliberate combinations of genetic material from organisms classified in different taxonomic genera. This review process is designed to prevent unreasonable risk of injury to human health and the environment without imposing unnecessary regulatory burdens on the biotechnology industry. The rule also established TSCA section 5(h)(4) exemptions from full reporting when 10 specific microorganisms are used as the recipient microorganisms for the introduced genetic material and placed requirements on these recipient microorganisms, the introduced genetic material, and the physical containment (40 CFR 725, subpart G). The rule established a mechanism (40 CFR 725.67) for the public to petition the Agency to propose additional recipient microorganisms for such exemptions. Those regulations also described the appropriate supporting information that must be submitted with the petition to provide the EPA with a starting point for determining whether the recipient should be listed as a candidate for the tiered exemption. The EPA received petitions to add Trichoderma reesei and Bacillus amyloliquefaciens to the list of microorganisms that may be used as recipient microorganisms in order to qualify for the exemption from full notification and reporting procedures under the TSCA for new microorganisms that are being manufactured (defined by statute to include import) for introduction into commerce. Based on the EPA's evaluation of these petitions, the EPA made a preliminary determination that certain strains of both microorganisms will not present an unreasonable risk of injury to health or the environment when used as a recipient microorganism provided that certain criteria for the introduced genetic material and the physical containment conditions are met and issued a proposed rule. After considering comments on its proposed exemption, the EPA is developing a revised proposal that will address the concerns raised by the commenters, and is considering expanding the earlier proposal to prohibit the inclusion of antibiotic resistance genes in the introduced genetic material in microorganisms qualifying for the TSCA 5(h)(4) exemption.