applications of nuclear technology where the primary control is placed on the design and use of the source. Since numeri- cal: values in the Guides were designed for the regulation of a continuing industry, they were of necessity set so low that the upper limit of Range II can be considered to fall well within levels of exposure acceptable for a lifetime. Further- more, to provide the maximum margin of safety, the upper limits of Range II were related to the lowest possible level at which it was believed that nuclear industrial technology could be developed a Obviously, guides developed primarily for use by industry in re- stricting its releases of radioactive effluents to the general environment outside their controlled areas are very materially lower than those that might constitute a serious health hazard. The last two points - the necessity of balancing benefits against risks and the establishment of radiation protection guides for the controlling of industry rather than for identifying a serious health hazard - have been two main sources of misunderstanding. They are subtle points to a layman and yet they must be understood if radiation fallout levels are to be properly evaluated. To relate hazards from one human enterprise to that of another is an abhorrent and controversial task and yet to do so may add some perspective to living in a 20th century world. For example, it has been reported that in one year's time (1962) approximately 600,000 children in the United States under 5 years of age accidentally swallowed toxic materials resulting in 450 deaths, and a much larger number of serious and crippling illnesses. Many other comparisons have been made such as our nation's annual death toll on the highway being 40,900 41.