Relationships between benthos and sedimentary organic matter quality were analyzed in the West Gironde Mud Patch (WGMP), on the shelf of the Bay of Biscay, off the Gironde estuary, as part of the multidisciplinary national programme Ecomarge, a JGOFS-France contribution. At three stations located on an east-west transect and at different periods from 1985 to 1988, the following parameters of the sediment were analyzed: POC (particulate organic carbon); SIGMA (sum of easily extractable macromolecules thought to be the most degradable part of particulate organic matter); pigments as indices of organic matter quality; ETS (electron-transport-system) activities and meiofauna densities as indices of benthic responses. Sediments from the WGMP have an overall low organic carbon content (0.8 %) ; the labile organic fraction (SIGMA) does not exceed 10 % of the total sedimentary POM (particulate organic matter). Nevertheless, the supply of freshly-formed matter was marked both by pigment and SIGMA increases, especially westwards. ETS activity was significantly linked to POC, SIGMA and chlorophyll a. The ETS: POC ratio was lower than in neighbouring coastal areas (i. e. the Gironde estuary and Arcachon Bay) but ETS: SIGMA_ was of the same magnitude in the three zones, reaching values close to ETS: SIGMA ratios found in live bacteria. It was concluded that SIGMA could mainly be composed of biomass itself; the detrital part of SIGMA, thought to be rapidly incorporated into living material, would not accumulate. The distribution of meiofauna abundances did not follow the same gradients as pigments, ETS and SIGMA, and presumably depended on environmental factors other than those analyzed here.