Thirty elements in 7 rat brain regions were determined by instrumental neutron activation analysis (INAA). The samples were irradiated by thermal neutrons using 3 different sets of conditions, depending on the nuclear characteristics of the elements. Analysis of the resulting radionuclides was by gamma-ray spectrometry using a high resolution Ge(Li) detector and Nuclear Data 6600 multichannel analyzer, which was fully computerized to give quantitative results for the gamma-ray spectra. This paper demonstrates the use of INAA for small biological samples and to show its potential elements, 7 rat brain regions are listed. It is interesting to note that certain elements, e.g. fluorine and potassium showed high and low regional differences respectively, and hypothalamus and hippocampus had higher elemental concentrations than other brain regions. However, since this paper is essentially an analytical one, no attempt is made to assess these data, which are preliminary, and the possible functional role of these elements will be discussed elsewhere.