[en] Just like in the western countries it might be necessary to reduce indoor radon concentration in Japan as well, since the potential exposure to radon and its progeny is comparable with the dose limits for stochastic effects for members of the public and radiation workers. It is not easy, however, to perform remedial measures for the reduction of radon exposure for the general population. Various problems related to scientific as well as political aspects have to be taken into account before any remedial action is put into practice. The aspects discussed here are establishment of screening method for radon measurement, identification of indoor radon sources, development of effective control measures, preparation of citizen's guide to radon, establishment of advice and information service, proposal of action level, foundation of an organization of measurement and remedial measures, clarification of the responsibility for the practice of remedial measures. The degree of urgency of these aspects deeply depends on the frequency of houses having relatively higher radon concentration. It might be necessary, however, to investigate and discuss the aspects cited above regardless of the results of the radon survey in Japan, since we have to take into account the present condition together with the future modification of our artificial environment which often results in the enhancement of radon exposure. (author)