This document aims to: a) assist in the choice and organization of inter-laboratory test comparisons for the application of proficiency testing; b) describe the elements that must be taken into account for proficiency testing; c) describe how proficiency testing can be used by bodies interested in the technical competence of testing laboratories. This document is intended for use by governmental or non-governmental organizations, such as accreditation and certification bodies, that evaluate the technical competence of testing laboratories. It can also serve as an aid to these laboratories in carrying out their own evaluation, admitting, however, that proficiency testing is only one of the numerous mechanisms that can contribute to the establishment of mutual trust between the different testing laboratories. rehearsal. This document does not provide details on the application of inter-laboratory assay comparisons.