To know the role played by marine sediments in influencing the fate of discharged metals, (1) the interaction of metals between sediments and deposit-feeder marine worms (Nereis japonica), and (2) uptake and excretion of metals by worms were examined by laboratory ex-periments using ^115mCd. Worms directly in contact with ^115mCd-sediments accumulated ^115mCd six times more than worms that were not in contact with the ^115mCd sediments during the 8 days of experimentation and 12% of ^115mCd in sediments were noted to be transfered to worms per unit. Comparing the concentration factor of 22 (from sea water) with accumula-tion from sediments, it was assumed that ^115mCd in sediments would give the effect of 1/200 to the accumulation of ^115mCd by worms in sea water to the accumulation of ^115mCd. Further, to simulate these results close to that occuring in the natural ecosystem, the distribution of ^115mCd in sea water, sediments and alga were also examined by means of a curve analysis of ^115mCd were 9 for sediments and 21 for alga, which was similar to 22 for worms.