Illnesses due to marine bivalvia consumption are mostly associated with viruses as causative agents. In more than the half of cases, this agent remains unidentifies, nevertheless. So far as bacteria are concerned, Salmonella are found firstly. Campylobacters represent a major cause of gastrointestinal disease, with Salmonella, among humans. Whether campylobacteriosis may be acquired from shellfishes remains unclear. We undertook to comparatively appreciate the survival of Campylobacter jejuni/coli and Salmonella typhimurium in seawater and contaminated mussels. Bacterial enumerations where performes using microbial cultures and specific (with immunofluorescence) direct viable counts (of substrate responsive bacteria). During laboratory contamination experiments, C. jejuni/coli and S. typhimurium are aforded together with unicellular microalgae Tetraselmis suecica. Mussels incorporate efficiently these microorganisms into their digestive tract (up 100 to 500 folds the concentration of contamination tank). In the gut of contaminated mussels, stored dry at 16 degree C, the number of culturable Salmonella remains constant after one week whereas C. jejuni persists in constant number of viable cells but exhibits a 10000 fold decrease of culturable bacteria. In seawater, Campylobacter survive poorly, compared with Salmonella: from comparable initial densities, the difference may reach a 106 factor after one week. The occurrence of mussel contamination with Salmonella is customary in polluted seawater: it should remain neglectible with Campylobacter. The cells of C. coli which survived after a 6 days stay into contaminated seawater and mussels maintained intacts virulence factors: mobility and adherence to cultured HeLa cells. This is at least true for bacteria remaining culturable, and questionable for viable non culturable cells. On the whole, shellfish born diseases due to Campylobacter should actually be possible (Griffin et al., 1983). This whould nevertheless represent a low probability because Campylobacter survive slenderly in seawater.