The Environmental Protection Agency (EPA) Office of Pesticide Programs (OPP) is participating in Organization For Economic Cooperation and Development (OECD) workgroups to update OECD guidelines number 201 (aquatic algal toxicity), number 208 (terrestrial plant toxicity), and to develop a new yet unnumbered guideline for the aquatic macrophyte Lemna spp. The EPA participants have presented the 850 series EPA guidelines and existing American Society for Testing and Materials (ASTM) guidelines to the OECD workgroups for their consideration. Under the existing North Atlantic Free Trade Agreement (NAFTA), the EPA is harmonizing plant toxicity tests and nontarget plant risk assessment methods with the Pest Management Regulatory Agency (PMRA), Canada. A pesticide regulatory workshop was recently held at the EPA to share information with Mexican government pesticide regulators. The OECD guidelines are focusing on pesticide and toxic substances, whereas NAFTA harmonization efforts to date are primarily for methods used to evaluate pesticides. While some of the plant tests are similar for toxic substances and pesticides, statutes and risk assessment methods are different.