The quality assurance system of the Quebec Ministry of Transport uses laboratory test results to evaluate the quality of bituminous concretes. The success of the system depends to a large extent on the reliability of these results. To evaluate on a day-to-day basis the reliability of the results, the Ministry developed a method to control the quality of laboratory tests based on the precision and accuracy of the test method used (that is, interlaboratory control) and on the reliability of results obtained by each laboratory (that is, within-laboratory control). The application of such a method has permitted the Ministry to obtain and even increase the confidence that the quality assurance system will succeed. It has also allowed the Ministry to detect and correct certain weaknesses attributed either to the test methods or the laboratories.