Concentration levels of eight trace elements in 120 samples of human blood serum were investigated by Instrumental Neutron Activation Analysis (INAA) for the purpose of medical research. The elements Co, Cr, Cs, Fe, Rb, Sc, Se, and Zn were simultaneously determined by the relative method in comparison with inorganic standards treated under identical conditions. The process of analysis and its reliability was checked using human serum and IAEA certified reference material. Statistical results are expressed in ppm or ppb. Both normal and, if necessary, log-normal frequency distributions of all elements determined are presented, types of distribution curves are verified statistically on 95% level of probability.