[en] Neutron activation analysis has become to be applied to the analysis of environmental contaminants in recent global environment problems, the quantitative determination of the matters that are related to the health of mankind and other living things and indispensable trace elements and so on in addition to basic research. The author has carried out the research on the quantitative analysis of the indispensable trace elements in bio-samples by activation analysis since 1965. The quantitative analysis of halogens, for which activation analysis maintains the usefulness as compared with other processes still today is outlined. The determination of fluorine in urine by photonuclear activation analysis, the determination of trace fluorine in biological materials by photonuclear activation analysis, the simple and rapid determination of iodine in milk by radioactivation analysis, the simultaneous determination of bromine and chlorine in cow's milk by radioactivation analysis, and the relation among iodine, bromine and chlorine in cow's milk in Japan are reported. All analyses were carried out by radiochemical technique, of which the sensitivity of detection is better, and the operation is simple and rapid. The objects of activation analysis for the future are pointed out. (K.I.)