it is evident that although the presence of a radioisotope from fallout can be detected easily by radiological methods the weight of the isotope is much less than can be detected by the most sensitive balance. For certain areas of the Atlantic Ocean the amount of sr?° delivered per unit area of sea surface has been calculated from the determination of sr?° in the surface layer and the depth of that layer. From analyses of the 1956 and 1957 data the amount of sr°° in surface waters was generally greater than for land areas at comparable latitudes of five between extremes (Libby, (Bowen and 1956) and varied by a factor Sugihara, 1957). The sr?? values for surface waters from the shelf area were the highest of any area and ranged from 6.3 to 30.0 disintegrations per minute per 100 liters of water. Begeman and Libby (1957) report the same general sort of variation in the analyses of Atlantic water for bomb tritium. Further study will indicate whether the fivefold variation of sr?° in surface waters is an artifact or the result of some factor in the circulatory system that prevents the surface waters from becoming thoroughly mixed. In deep ocean water, below 800 meters, the values for sr?° were less than 10 per cent of the surface values. Selection of the other four radioisotopes--sb! 2°, cst 37, cel44 and pm! 4? __was based on the fact that their relatively long half lives and relatively high ydelds in fission gave promise that