I. INTRODUCTORY Ritu.KKS aND GUMMARY Of 02.0 IMUNY To the general public, the most important question about fallout from nuclear tests is: “what is the risk of medical harm to the popuiation as a result of fallout; if there is a risk, what can be done to reduce it?" wince its inception, the United States program of nuclear tests has included a considerable effort to determine the deposition of fallout outside the actual test area, to estimate the possible medical hasard of such fallout to persons exposed to it, and to warn of needed countermeasures when the occasion arises. Contributing to this effort has been the work of the AEC, the agency directly responsible for nuclear test operations, the U. S. hublic Health Service, and the hearings conducted by the Congressional Joint Committee on Atomic Energy. Two separate aspects of the problem need to be considered: (a) The medical risks to the tota] population resulting from the widespread dissemination of radioactivity from tests which occur anywhere in the world. (b) The medical risks to docal populations, resulting from relatively short-range fallout which spreads rapidly from the test site in Nevada to surrounding communities, and sometimes - depending on weather condi- tions - to dixntan*: areas in the continentai United States. The first of these p.o»' ens has been given extensive consideration recently; the St. ‘.uis Citizens' Committee for Nuclear Infor mation (CNI) has previously submitted extensive testimony relevant to it.