Sample Collections and Analytical Results During 1976, 50 liter unfiltered seawater samples were obtained from lagoon locations 1, 5, 7, 8 and 10 shown in Fig. 1. duplicate locations sampled during 1975. Stations 1 and 5 Between 1975 and 1977 surface seawater samples were collected at several open ocean locations within the area of the Northern Marshall Islands. Plutonium and cesium were separated from the water samples and the concentrations of 23942405, and 1376, were determined using published methods (Wo 78, Wo 71). Our analytical results are shown in Table 1 along with 1975 lagoon seawater concentrations previously reported (No 76). In a few samples where the 2385, concentrations were above our detection limits, were computed and are given in Table 1. the 2385, /73942405,, ratios For comparative purposes, concentrations in surface seawater samples collected in the north equatorial Pacific since 1972, in Table 1. from the cited references, are also compiled At one ocean surface station where the particulate material collected onal um filter was analyzed, the concentration of 23942405, associated with the filtered material represented 13% of the total concentration in the water. Eighteen mullet (14 female and 4 male), Crenimugil crenilabis, were collected on October 21, at Kwajalein Atoll. 386 mm. 1976 from the lagoon reef off Enewetak Island The standard length of the fish varied from 265 to Reef fish collected from this island in 1972 (Ne 73) had the highest reported plutonium body burdens at Kwajalein Atoll. Mullet are primary consumers and represent species belonging to the second trophic level. Guary and Fraizier (Gu 77) maintain that concentration factors for E LUIVES DOE AR