Sodium contents in seven mixtures of biological materials from varying aliquants of wheat flour and oyster tissue were analyzed using the INAA (instrumental neutron activation analysis) method. The samples were activated in the thermal column (TC) of the 1 MW TRIGA reactor at our laboratory. To analyze and compare the measured results, the ratioa of the epithermal neutron flux to the thermal neutron flux was determined in the TC, the rotating rack (RR) and the pneumatic terminal (PT). Due to the negligible interferences of24Mg(n, p)24Na and27Al(n, )24Na to23Na(n, )24Na, the Na results were obtained with 97% accuracy and 99% precision. It is shown that the method is suited for accurately determining Na contents in 12 various biological materials, especially for the samples that are low in Na content. From the cadmium ratio measurements of Au (4.9 eV resonance of198Au) and Sm (8 eV resonance of153Sm), ratios ofae/0 were determined at 0.0011, 0.052 and 0.053 in the TC, RR and PT activation positions, respectively.