The paper summarizes the work done by the Institute of Nuclear Chemistry and Technology, Warsaw (INCT), in the field of QA/QC with the special emphasis on the role of NAA. This work consists of preparation and certification of CRMs, development of high-accuracy RNAA methods for selected elements in biological matrices and organization of proficiency test rounds (PT). The INCT has been involved in the preparation and certification of CRMs for inorganic trace analysis since 1986. The adopted certification philosophy is presented. Comparison of analytical data on the same material available from interlaboratory comparisons organized in different years is presented. The paper summarizes also the work on the development of high-accuracy RNAA methods. It has been demonstrated that the high-accuracy RNAA methods devised according the concept formulated in INCT can meet requirements of primary ratio method of measurement (PMM).