Different types of denitrification rates in coastal marine sediments from the Western Mediterranean coast (France) were simultaneously determined by varioUS C2H2 inhibition techniques: in situ denitrifying activity in intact cores or sediment slurries; DEA (Denitrifying Enzyme Assays); and potential activity. Denitrifying activity was also estimated by the use of kinetic parameters (Km and V(max)). Values for denitrifying activities in the top two centimetres ranged from 0 to 50-mu-moles of nitrous oxide produced per litre of sediment per day, and were similar when intact core or sediment slurries were used. DEA showed comparable values for all the study sites. The potential activity ranged from 298-600-mu-moles per litre per day. Estimated activity based on kinetics parameters was between 0.4 and 2.5 % of the denitrification potential. Estimation of denitrifying activity based on kinetic parameters and in situ NO3- concentration thus seemed impossible.