During spring of 1993, an epizootic outbreak occurred in a sea bass farm, located on the French Mediterranean coast. The cumulative mortality reached 25%. First examination of cutaneous lesions revealed filamentous bundles of flexuous bacteria which exhibited gliding motility. Bacterial growth was obtained only from skin lesions. The biochemical characteristics of isolates are described. Pathogenicity tests of representative slrains were carried out. Until fuller data is available, the pathogen here reported was provisionally identified as a Cytophaga·like bacterium (CLB).