This standard@ ANSI0ANS-16.1-2003@1) provides a uniform procedure to measure and index the release of radionuclides from waste forms as a result of leaching in demineralized water for 5 days.2) The results of this procedure do not apply to any specific environmental situation except through correlative studies of actual disposal site conditions. The test presented in this standard has much in common with the original International Atomic Energy Agency proposal and has by now become familiar to those working in the radioactive wasteform development f ield. It contains the provisions published in the original version of this standard in 1986. Purpose The quantification of the leaching characteristics of solidified wastes requires a standardized@ practical method to measure the ability of the solids to impede the release of radioisotopes when water comes into contact with them. The purpose of this standard is to establish such a test@ define a material parameter@ and provide a mathematical procedure for calculating a ??Leachability Index?? value for the test data collected over the time period of the test. This standard is intended to serve as a basis for indexing radionuclide release from solidified low-level radioactive waste forms in a shortterm (5-day) test under controlled conditions in a well-defined leachant. It is not intended to serve as a definition of the long-term ~several hundred to thousands of years! leaching behavior of these forms at conditions representing actual disposal conditions. Under actual leaching conditions@ mechanisms other than diffusion (e.g.@ chemical reaction@ surface layers and films@ cracking@ etc.) are important considerations. Also@ the interplay of retardation mechanisms (f iltration@ ion exchange@ coprecipitation@ etc.) and enhancement mechanisms ~chelation@ desorption@ dissolution@ etc.! for radionuclide migration are important considerations.