Microbial activity acts as primer in the self combustion process of solid recovered fuels (SRF) during their storage or transport. Thus, EU gave mandate to the European Committee for Standardization (CEN) to develop biological methods, (i.e. respirometric method) able to assess the risk of potential self combustion of SRF. Real Dynamic Respiration Index (RDRI) was chosen as official method, and a validation procedure was requested, to assure the quality of the results, when the method is applied for official purpose, i.e. repeatability and reproducibility detection. Two SRF coming from full-scale plants were analyzed for RDRI by three laboratories in six replicates. Results indicated a good precision of the method proposed in agreement with other biological methods, i.e. relative standard deviations of repeatability ranged from 16.7% to 17.8%, and a relative standard deviations of reproducibility ranged from 17.5% to 23.9%. (C) 2010 Elsevier Ltd. All rights reserved.