Introduction. In 2002, the Concept for reforming the clinical laboratory diagnostic service was approved in St. Petersburg. It provided for centralized implementation of laboratory investigations. However, the results of the centralization carried out for the needs of primary health care within the compulsory medical insurance have not previously been considered in the available literature. The aim of the study is to analyze the features of the clinical laboratory diagnostic service centralization in metropolis (St. Petersburg experience) in the organization of primary health care within the compulsory medical insurance system. Materials and methods. An analysis of the medical laboratories activities, which provided investigations in primary health care during 2016-2021, was carried out according to the register of accounts of the EIS OMS of St. Petersburg. A grouping of Interdistrict Centralized Clinical Diagnostic Laboratories (ICCDL) has been conducted according to the volume of tests performed in 2021 using the Sturges rule. The direction and strength of relationship between the volume of tests performed by ICCDL and the number of assigned medical organizations, as well as attached population have been determined using the Spearman rank connection method. Results. 13 ICCDL performed 85% of the total number of laboratory tests in primary health care in 2020. However, low-power laboratories of some medical organizations assigned to the ICCDL continue to exist. Among the ICCDL themselves, there is differentiation in distribution by administrative districts, the number of assigned organizations, the level of subordination and the volume of tests performed. At the same time, all ICCDL of St. Petersburg may be identified as the 2nd level laboratories. High-tech and unique investigations of the third level are carried out in large multidisciplinary medical organizations, as well as in private laboratories. Discussion. The St. Petersburg experience shows that centralized laboratories can be successfully organized on the basis of a municipal polyclinics. However, the issue of uneven distribution across administrative districts as well as lack of a single administrative subordination of the created ICCDL requires additional study. The priority task should be considered the liquidation of the remaining low-power first level laboratories, which should be preceded by the improvement of some types of tests technologies, in particular using manual methods and capillary blood. The participation of private and federal institutions’ laboratories in the provision of primary health care makes it possible to use their capacities to perform high-tech and specialized research, but it raises the issue of a 3rd level ICCDL formation in the regional health care system. Conclusions. An analysis of the clinical laboratory diagnostic service organization in St. Petersburg confirmed the naturally-determined shortening of the laboratories number in primary health care and the leading role of the ICCDL in the diagnostic process. Centralization of laboratory diagnostics makes it possible to increase the technological accessibility of routine laboratory testing for the population. But the identified features do not allow us to consider centralization as a completed process and lead to the need to audit the existing system with special attention to the methodology and tools of centralized planning and development laboratory network.