Polychaete prey were studied in the diet of 16 demersal fish species caught during an evaluation survey of demersal resources in the southern part of the Bay of Biscay during autumn, year 2000. A total of 27 prey taxa belonging to 17 families (21 of them at the species level) were found. Mullus surmuletus appeared as the main polychaete specialist. The consumption of polychaetes in other species, such as Pagrus pagrus, Chelidonichthys obscurus, Raja montagui, Scyliorhinus canicula, Trachyscorpia cristulata equinata and Pagellus acarne, was also important. Four species were analysed in more detail, M. surmuletus that preyed mainly on the families Nephtyidae, Sigalionidae and Goniadidae, P. acarne on Sigalionidae, R. montagui, on Sigalionidae, Arabellidae, Glyceridae and Aphroditidae, and S. canicula on Arenicolidae, Nephtyidae and Arabellidae. The most frequent species found in the stomachs were Nephtys hombergii, Aponuphis bilineata, Labioleanira yhleni, Arabella iricolor and Laetmonice filicornis. The predators had a clear preference for errant and carnivorous polychaete species, probably due to the more active behaviour of these prey, and also as a result of trawl fishing.