~ 48 - define; and near the end of the survey, off the coast of Japan. At the present time the radioisotopes may be dis- tributed more thoroughly in the North Pacific circulation system than in 1954 but the levels of radioactivity would be generally comparable. Recent determinations have been made of sr9° in sea water from the western North Pacific and North Atlantic. For the Pacific, Miyake et al. (1960) reported 2 to 5 d/m/1 for six samples collected in 1957, 1958 and 1959. The values for eleven samples collected in 1956 and 1957 in the Atlantic were about one-tenth the Pacific values and ranged from .06 to 0.3 d/m/1 (Bowen and Sugihara 1958). Larger values in the Pacific were not surprising because of the contribution by local or close-in fallout from Bikini- Eniwetok. Measurement of Sr99 in waters of the eastern North Pacific have not been made; however, there has been time for the long-lived isotopes from local fallout at Bikini- Eniwetok to reach the eastern Pacific by ways of the current system. As a result of the surveys following the weapons tests at Bikini-Eniwetok in 1954, 1956 and 1958, 4t is known that the areas of contamination can be identified by measuring the radioactivity in the water or plankton but more easily in the plankton, and that the radioactivity moves westward from