SummaryResults of the Belgian proficiency surveys (1971–1973) for clinical chemistry labs are reported. The specific position of this external type of quality control is analyzed. Special attention is given to the detection of systematic factors that could interfere with the introduction of a uniform medical record.A new procedure is described for displaying results grouped according to methods. The difference between the main methods in actual use is of the systematic type rather than a difference in precision.The Youden approach to collaborative tests has been elaborated and generalized by the introduction of correla-tion as an expression of the incidence of systematic factors. The shape of the contour encompassing 95% of the Youden couples, defines a target area often very different from the circular surface expected with uncorrelated results.The participating laboratories, as a group, appeared to work from the beginning according to the current state of the art. Improvement is only possible if basic changes in methods or in calibration are introduced. This suggests a broadening of the activities of the Belgian Society for Quality Control.