A follow-up study has been made to assess the concentrations of 239+240Pu and 137Cs in the marine environment of Kwajalein Atoll. Fish collected from the atoll in 1972 had body burdens of plutonium that were substantially higher than concentrations in similar species from locations contaminated only with global fallout. Our recent results, however, indicated that Kwajalein lagoon seawater contained levels of plutonium more similar to global fallout levels found in north equatorial Pacific surface waters. No satisfactory explanation for the reported plutonium levels in fish from Kwajalein collected in 1972 could be deduced from the available data. The highest plutonium concentrations reported for the 1972 reef species of fish could expose man, through ingestion of marine foods, to a dose rate as high as 25% of the proposed EPA guideline for annual total transuranic dose rate to bone (3 mrad/yr over 70 yr). Our present results show the dose rate from the marine food pathway is nearer to 0.005% of the recommended EPA value and is consistent with the view that Kwajalein Atoll contains plutonium concentrations that are expected from global fallout. The magnitude of the plutonium levels reported in fish collected from Kwajalein lagoon during 1972 was excessively high, and these results appear to be inconsistent with other environmental data from the lagoon. Our results also show that concentration factors for plutonium in fish muscle and bone tissues appear to be independent of species, trophic level and location, which leads us to believe that there is a great deal of validity in the concept of a concentration factor for estimating concentrations of plutonium in fish.