The Organization for Economic Cooperation and Development (OECD) has established a set of guidelines for the testing of chemical substances to determine their impacts on human health and environmental safety. The OECD set up the Working Party on Manufactured Nanomaterials (WPMN) (37) in 2006 to assess the potential impacts of nanomaterials on human health and environmental safety and to assess whether or not existing guidelines could be applied to nanomaterials. An initial review completed in 2009 determined that the existing guidelines were valid for nanomaterials, but that in certain cases modifications would be necessary for the guidelines to be applicable. Projects are underway to develop new guidelines and modify existing ones, such as the inhalation toxicology guidelines.