This paper presents and discusses the results of Pu239+240 determinations in different components of Gdansk bay and Gdansk basin ecosystem, as well as estimated sources and inventories of plutonium in these basins. The total plutonium Pu231+240 activities deposited in Gdansk bay and Gdansk basin sediments are 1.18 TBq and 3.77 TBq, respectively. Two rivers, the Vistula and Neman rivers, and atmospheric fallout were distinguished as the main sources of plutonium in these basins. In seawater (with suspended matter included) there is about 2.33 GBq Pu239+240 (0.2% of total activity) in Gdansk bay and 9.92 GBq Pu239+240 (0.3% of total activity) in Gdansk basin. In both cases, 56% of Pu239+240 is associated with suspended matter. Organisms contain 3.81 MBq in Gdansk bay and 7.45 MBq Pu239+240 in Gdansk basin. From this value in Gdansk bay 82.1% of plutonium is associated with zoobenthos, 13.6% with phytobenthos, 1.6% with phytoplankton, 1.5% with zooplankton and 1.2% with fish. In Gdansk basin, 83.2% is associated with zoobenthos, 7.5% with phytobenthos, 3.6% with phytoplankton, 3.2% with zooplankton and 2.5% with fish. (C) 2003 Elsevier Science Ltd. All rights reserved.