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This work describes the outcomes of the COST Action-TU1301 “NORM4Building” intercomparison on the determination of natural radioactivity in ceramics. Twenty-two laboratories involved in the intercomparison are evaluated for their performance using robust statistics. The reference values of 226 Ra ( 214 Bi and 214 Pb) are determined to be 122 ± 11 Bq kg −1 and 124 ± 14 Bq kg −1 , respectively and in secular equilibrium in the uranium chain while the reference values of 232 Th ( 228 Ac) is determined to be 61 ± 6 Bq kg −1 and that of 40 K was determined to be 955 ± 40 Bq kg −1 . Although the aim of the exercise was to determine the activity concentration of 226 Ra, 232 Th and 40 K and evaluation of the “Activity Concentration Index”, laboratories were asked to report complete characterization of natural radionuclides. The results of this exercise pointed out a good performance among laboratories since the percentage of the acceptable results were above 90% for the radionuclides of interest. Based on these results, considering the systematic rejection of the results reported from a few laboratories we emphasize the need for quality control procedures. [ABSTRACT FROM AUTHOR]