[en] Instrumental neutron activation analysis (INAA), which is one of the analysis methods with the highest sensitivity, has been used to determine trace elements in environmental, biological, geological samples and so on. We have developed since 1975 an automatic γ-ray spectrometry systems for neutron activation analysis with our TRIGA-II research reactor. These systems are named the GAMA (Gamma-spectra Analysis of Musashi Institute of Technology, Atomic Energy Research Laboratory). These systems are fully on-line from the acquisition of a spectrum to the analysis of data, allowing the precise routine analysis with easy operations. The analytical program of acquired data was performed automatically from peak search and peak analysis to determination of elements. In order to show the performance of our neutron activation analysis, some kinds of samples were analyzed. The samples were analyzed with combination of four neutron irradiation methods and four γ-ray counting methods, to determine as many trace elements as possible with high sensitivity by using the GAMA system. We could determined 52 elements in a vehicle exhaust particulates environmental reference material by combining different irradiation and counting methods. Selenium in thirty five kinds of soybean samples was determined with three counting methods. The Se contents of soybean samples were found to be in range of 5 - 300 ppb. Water samples taken from 15 points of the Tama River were activated by a solution directly activation method. Twenty-five elements were determined by this method. (J.P.N.)