Denitrification was measured in the sediments of the Inner Puck Bay using the acetylene inhibition technique and pertinent environmental data. This process was not found to be particularly significant for the nitrogen budget of the ecosystem. The rate ranged from 0 to 40.2 mmol N m-2 h-1, which is equivalent to 151 t N per year. This constitutes 6.5% of the external nitrogen input to the investigated water body. The denitrification rate reached the highest values in spring, after the first algal blooms, when relatively fresh organic matter had amassed in the sediments and nitrate concentrations in interstitial waters peaked. The rates were almost sixfold lower than the maximal value in summer and fall. The main nitrogen source for denitrification in the investigated area was nitrification within the sediments. The deciding parameter determining the variability of the denitrification rate was the nitrate concentration in interstitial waters.