Sediments from the BIOTRANS area at 47°N 20°W in the NE Atlantic (4500 depth) were supplied with particulate and dissolved organic matter from sterilized net plankton and incubated under in situ pressure and temperature. Changes in the potential hydrolytic activities of extracellular enzymes were observed over a 15 d period. Induction of enzyme production proportional to the supply of organic matter was found for enzymes degrading structural polysaccharides while aminopeptidase activity was inhibited and no clear effect was found for enzymes degrading storage compounds. Particulate organic matter induced higher enzyme production than equivalent amounts of dissolved organic matter. Only a slight increase in microbial biomass was observed, indicating that changes in enzyme activity were not due to bacterial growth. -from Authors