As the national metrology laboratory in the field of ionizing radiation and because of its forty years of experience in organizing interlaboratory tests, the LNHB was asked by laboratories participating in IRSN  regulatory tests to organise preparation tests. Since 2003, ASN and IRSN have had the mission of leading and managing the acute au National de Mesures  National Network of Measures (RNM) instituted by articles R. 1333-11 and R. 1333-11-1 of the Public Health Code). Radiological analyses of environmental samples are therefore carried out by IRSN and approved laboratories. Approvals are granted on the basis of quality and technical criteria: in particular, if satisfactory results are obtained in the multiannual intercomparison tests organised by IRSN. The various interlaboratory tests are programmed by type of environmental matrix and by category of radioactive measurement according to the accreditation grid approved by the ASN. There are thus 6 families of environmental matrices (water, soil, biological matrices, aerosols, etc.) and 17 categories of radioactive measurements (tritium, alpha global, beta global, radionuclides emitting γ radiation > 100 keV, etc.), representing 52 approvals. The results of the tests are analyzed by an approval committee. A deviation of more than 25% from the reference values shall result in withdrawal of approval. It was therefore important to allow approved laboratories to test and improve their performance prior to regulatory testing.