Plutonium 239,240 was measured using large-volume water samples from the North Pacific and its adjacent seas. The vertical profiles of239,240Pu show features that are similar to those reported in earlier papers with a subsurface maxima of around 660 m and a significant concentration increase in the North Pacific bottom waters. It became evident that the239,240Pu concentration in deep bottom water is proportional to the inventory of the nuclides in the overlying water column and that the appearent distribution ratios of the nuclides between deep-sea sediment and bottom water lie in a relatively narrow range of about 2×104 to 105, independent of sea area and warter depth. The latter implies that239,240Pu may follow a reversible-type partition process at a deep water/sediment interface. In order to substantiate this assumption, it is desirable to study the phenomenon for Pu as well as for other long-lived radionuclides, both artificial and natural. From this point of view, an analytical procedure for the successive determination of selected long-lived radionuclides was studied.