Fifty sandworms, Nereis virens, were maintained in a closed aquarium system with continuous charcoal filtration at 12 degree C and 27.6 ppt S. They were dosed orally for 10 consecutive days with a mixture of three pentachlorobiphenyls: 35 ng 2,4,6,2',4'-pentachloro(U- super(14)C)biphenyl, 106 ng 2,4,5,2',5'-pentachlorobiphenyl, and 106 ng 2,3,4,2',5'-pentachlorobiphenyl per g of Nereis virens per day. At the end of the dosing period the accumulated compounds were measured in 5 worms, the remaining 45 specimens were divided into three groups for determining the PCB elimination under different conditions for 14 to 26 weeks: in the laboratory with feeding, in the laboratory without feeding, and in a cage moored in the Weser estuary.The accumulation percentage for these PCB compounds were 41, 26 and 4% respectively. Times for the initial 50% decrease t sub(e)50 were 4.4, 2.8 and 1.9 weeks respectively, and appeared the same in all three experimental groups. However, in the laboratory experiments the metabolites of the super(14)C-labelled compound amounted to similar to 60%, compared to the field experiment with similar to 30%. This extended the t sub(e)50 for super(14)C activity (metabolites included) to similar to 9 weeks in the laboratory experiments.