Nematodes are the most abundant multicellular animals in marine sediments; they are also the only metazoans, which survive in heavily polluted areas. The seasonal fluctuations of the nematode community of a heavily polluted silty sand station along the Belgian east coast was examined based on the monthly samples during 1983-1985. The mean density of the total community varied between 55 ind./10 cm 2 (Feb.1983) and 5610 ind./10 cm 2 (Jun.1985). 32 species were found in this station; only four species have a frequency higher than 50 %. They are all non-selective deposit-feeders. Reproduction appeared to be continuous, although an increase in reproductive activity appeared in spring and autumn. The seasonal fluctuations of density, age structure and the yearly P/B were determined for Sabatieria punctata, Daptonema tenuispiculum, Ascolaimus sp.1 and for the whole community. The yearly P/B for S. punctata varies between 14.1 (1985) and 16.9 (1983); for D. tenuispiculum between 28.5 (1985) arid 31.9 (1983); for Ascolaimus sp.1 between 11.5 (1985) and 14.8 (1983) and for the whole community between 16.2 (1985) and 18.1 (1983). These are the first estimations of P/B ratios for nematode communities in the Southern Bight of the North Sea. From this, it appears that nematodes are a significant component in the energy flow of shallow water ecosystems.