Recent ^{239, 240}Pu and ¹³⁷Cs concentrations in some marine biota collected mostly from the seas around Japan were determined. Ash samples were digested with hot nitric acid, and the radionuclides were purified by ion exchange processes, then their alpha and beta radioactivitieswere measured.
^{239, 240}Pu concentrations were in levels of 1/10 to 1/100 of ¹³⁷Cs concentrations, and showedvalues of some pCi/100 kg-raw in muscles. No clear difference was observed in the contents of the radionuclides of muscles between shallow waters and deep bottom inhabitants.
Considerahle variation in ^{239, 240}Pu concentrations were shown among organs and tissues, but ¹³⁷Cs showed no such discrepancy.
Apparent high concentration factors(CF)for ¹³⁷Cs of the deep water inhabitants were sup-posed to be caused by the contribution of the food chain in the deep sea.
Concentrations of the radionuclides in krill and fur seal were also discussed.