AbstractThere are many classic experiments on the effects of radiation on cells in culture and on small mammals. These, together with anecdotal data on radiation effects in humans establish the carcinogenic hazard which by now is well known, even to laymen. Although a certain amount of radiation exposure is unavoidable, the number of applications of radiation in medicine is constantly increasing. Nuclear power plants now supply a little less than 10% of the electrical power in the United States. In order to draw up a reasonable balance between costs and benefits of radiation we must be able to measure and assess these costs. In this paper, Dr. Mossman discusses the current state of knowledge relating to the carcinogenic risks of radiation. This includes a breakdown of the known types of cancers in man and their relation to radiation exposure. Also discussed are some of the problems in risk assessment, and in particular that of determining effects of low dosage. This a major stumbling block in the measurem...