High-quality human body material (HBM) samples are required for valid scientific research. However, the effects of long-term sample storage on their future research potential are not well-known. Particularly for HBM samples studied in the context of human infectious diseases, an important domain of expertise of the Belgian health institute Sciensano. The objective of this project is to evaluate the fitness of long-term (> 1 year) stored HBM samples at Sciensano for their potential use in future research concerning human infectious diseases of interest to Sciensano. Depending on the HBM sample type, these samples are stored in (ultra-)low temperature freezers or cryo-tanks, several of them already for many years. An extensive literature study on this subject has been performed and the gaps of knowledge were identified. In this project, samples that have been positively analyzed in the past at Sciensano for a pathogen of interest, will be evaluated. The applied quality control biomarker to evaluate the fitness will be the loss of assay positivity per storage year, determined after re-analysis of the samples according to the assay that was applied for obtaining the initial study or diagnostic / surveillance result. Different assays (PCR, immuno, …) will therefore be used. By comparing the previously obtained assay results of the selected HBM samples with their re-testing results, the duration of long-term sample conservation without loss of quality can be assessed. This will lead to the setting-up of guidelines on storage duration of our HBM samples, depending on the sample type and pathogen analyzed.