[en] For analytical methods to be applied to international safeguards, precision and accuracy must be well established. With this objective an interlaboratory measurement evaluation program - ''IDA-80,'' which determined the elemental and isotopic content of the input solutions to reprocessing plants - was carried out with the participation of 33 laboratories from 15 countries or international organizations. It was guided jointly by the Central Bureau for Nuclear Measurements (CBNM) and the Kernforschungszentrum Karlsruhe (KfK) under the auspices of the European Safeguards Reseach and Development Association and with the support of the International Atomic Energy Agency. The element concentrations and isotopic compositions of all test materials were characterized by CBNM and the U.S. National Bureau of Standards to a high accuracy