A calibration service was introduced in 1986 to assist the Canadian nuclear medicine community in determining more accurately the amount of radioactive material administered to patients for either diagnostic or therapeutic purposes. This aspect of a quality assurance program in nuclear medicine provides an accuracy check on instruments and the technologists using them. The calibration report issued constitutes direct traceability of a facility to a national standards laboratory. Nuclides most frequently calibrated are 99mTc and 131I. Others include 67Ga, 111In, 123I, 125I and 201Tl. All samples received are analysed for radionuclidic impurities by high-resolution X-ray and gamma-ray spectrometry. Ten years of testing has shown that, except for a few conscientious departments, accuracy checks on radionuclide (dose) calibrators are not a high priority. There are 285 nuclear medicine facilities in Canada and, since there is no legal requirement that the calibrators be checked for accuracy, only 29 have had their instruments checked using this service. Of these, 14 perform annual accuracy checks with NRCC. In this paper, the results of the intercomparisons are described, and quality control problems associated with the use of radionuclide calibrators in nuclear medicine are discussed.