[en] Among other functions, the Pacific Northwest Laboratory (PNL) tests and calibrates instruments and dosimeters that are used to measure the quantity of radiation to which workers may be exposed. One of the projects that is carried out by PNL's Health Physics Department is the operation of a proficiency testing laboratory for radiation dosimeters. This paper describes the capabilities and the operational details of the laboratory. In order to perform its tasks, it is essential that the laboratory have a wide range of radiation sources along with the testing apparatus necessary to assure the quality of instrument and dosimeter performance. It is also necessary to demonstrate that instrument and dosimeter calibrations are consistent with national standards. 5 refs