The Environmental Protection Agency has proposed a long-awaited rule that would, for the first time, define how it will regulate genetically modified organisms under the Toxic Substances Control Act (TSCA). The agency also has issued a final rule governing field testing of microbial pesticides developed by genetic modification. In a rare moment of unanimity, environmental and industry groups applauded both actions.The proposed rule formalizes EPA's current system for screening microorganisms. It defines as new chemical substances, subject to TSCA notification requirements, microorganisms formed by combining genetic materials from organisms in different genera. The rule requires persons intending to manufacture, import, or process intergeneric organisms for commercial purposes to file a Microbial Commercial Activity Notice (MCAN) with EPA at least 90 days before undertaking such activity. Introduction of such organisms into the environment for commercial R&D purposes requires 60 days' advance notific...