years, the remains of the Eugen are still contaminated and small quantities of plutonium are continuously remobilized to the water column near this source. However, if this should be the case, the amount remobilized is not in sufficient quantities to alter the average lagoon water concentration above fallout background levels. Since 1972 the average surface seawater fallout concentrations of 23942405, in the north equatorial ocean have varied by no more than a factor of 2. The variations in surface concentrations are due to differences in the rates of new atmospheric fallout to the sea surface and to processes moving plutonium laterally and to depths in the water mass. We can assume that variations in the concentrations of plutonium no larger then those encountered in the open ocean since 1972, occurred in the lagoon water mass. To summarize, the mean water concentration of 23942405, in Kwajalein lagoon during 1975 and 1976 was slightly higher, but not outside the statistical uncertainity associated with the average global fallout levels in northern equatorial surface waters. 1975 and 1976 north equatorial surface concentrations of plutonium were similar to the levels detected during 1972. 2385, 23942405, ratios measured in the 1976 water samples from the ocean and lagoon were similar in value which indicates that the radionuclides were derived from the same source. The upper 11 cm of sediment from one area of the lagoon contains a plutonium inventory within the range of the fallout inventories measured in the water columns of the north equatorial Pacific. We conclude that global fallout is the principal source of plutonium and cesium radionuclides found in the Kwajalein lagoon environment. nc?r N actives