Current events of clinical laboratories in France argue a lot about quality management. Setting up an assurance quality system can be realized in many approaches listed by increasing requirements: respect of reglementary Guide de bonne exécution des analyses (GBEA), BioQualite qualification, certification and at last accreditation. This last step corresponds to the recognition of the competence of the laboratory to execute specifics tasks. Validation of methods used in the laboratory is a key point when you realize an accreditation package. Fidelity (repetability and reproductibility) is one of the parameters to check in your lab for quantitative methods. These performances are validated in comparison with targets beforehand defined (according to biological variation or state of the art). This article reports fidelity performances obtained in 2000 and 2006 by the participants to ProBioQual internal quality controls. Considering these performances obtained in routine conditions, the different possible approaches to define acceptability limits were discussed.