Leaching tests are conducted according to different standards, pro cedures or recommendations, generally under conditions different from those of the disposal media. Such tests are generally useful for com paring various containment matrices to ensure maximum isolation of radionuclides, and allow waste conditioning processes to be optimized. However, when defining release hypotheses to be taken into consideration for risk analysis, these methods can often lead to hypothesis which are either too optimistic or too pessimistic. The uncertainties basically involve the processes by which containers deteriorate during transport, handling and utlimate storage. Moreover, the interpretation of test results must be more clearly correlated with the known physico-chemical mechanisms involved. In attempting to find an answer to this question, tests have already the recovery been undertaken, including the use of lysimeter devices or of waste materials after several years of storage. The aim of the seminar was to exchange views among experts in characterization, waste management and safety analysis for the purpose of defining the principal actions that could be undertaken or of reorienting ongoing studies in order to limit the uncertainties involved."