Wiile there has been little investigation of specific defense measures which might be feasible, it appears reasonable to assume that the hazards from any one aspect of radioactive fallout could be greatly reduced by appropriate defensive action. Strontium” is still considered to be the most probable critical factor. Dr. Western brought out that there are many unanswered questions related 0 to hazards from strontium’ - . He said that the distribution of strontium” in local fallout and the stratosphere are poorly known. Also poorly known are the actual concentrations of strontium 90 in the human skeleton necessary to produce various biclogical effects. A program to obtain better biological data in large mammals, using dozs, is being initiated. The Sunshine program of assaying the occurrence of strontium” in the biosphere has progressed sufficiently to permit a semi-quantitative estimate of the ratio between the fal’out of strontium” and the occurrence of strontium?” in the skeletons of persons living in areas of general fallout. This ratio is based on direct observation of concentrations in soil and bone samples in a particular geographical area, and might vary considerably with varzvation in such conditions as dietary habits, soil characteristics, desiyn and use of weapons, and protective measures. Dr. Western states further that the highest percentages of strontium observed in human bones in the United States are of the order of one= thousandth the maximum permissible value for occupational exposure to strontium”” 90 currently recommended by the International Commission on radiological Protection and by the United States National Committee on Radiation Protection. - 13 =