[en] External evaluation of laboratory results and procedures can be carried out by participation in intercomparison exercises. For this purpose the Neutron Activation Analysis (NAA) Laboratory at PINSTECH participated in the International Atomic Energy Agency - Marine Environmental Laboratory (IAEA-MEL), Monaco intercomparison exercise IAEA-158, marine sediment, IAEA-CU-2006-06 Proficiency Test (PT) on 'The determination of major, minor and trace elements in ancient Chinese ceramic' and IAEA intercomparison on 'Trace elements and methyl mercury in fish scallop: IAEA-452'. After receiving the final reports of the PT and intercomparison exercises, a critical review of our data and final scoring of each element was made to check the suitability of our methodology and reliability of the acquired data is shown. Most of the reported results passed different statistical evaluation criterion such as relative bias, z-scores and u-scores and ratio of our results and IAEA target values. It was concluded that the elements for which unacceptable results were obtained were for those which had higher uncertainties cited by the RM producers. To overcome these issue additional synthetic standards for these elements along with the usual RMs with lower uncertainties may be used. (orig./A.B.)