Vibrios are autochthonous in estuarine and seawater environments, and have an important role in the decomposition of both particulate and dissolved organic matter. A considerable number of pathogenic strains have been described, including important human pathogens. Analyses of V. cholerae, V. parahaemolyticus and V. vulnificus genes in blue mussels (Mytilus edulis) from southern Sweden were conducted during summer-autumn 2006. 61% of the samples were positive for non-O1/O139 V. cholera (toxR positives), but all were negative for the choleratoxin gene ctx. 89% of the mussel samples contained V. parahaemolyticus and 61% of these were positive for the virulence genes tdh and trh. V. vulnificus were detected in 72% of the samples. Ongoing studies include analyses of Vibrio-phytoplankton interrelationships and survival of clinical Vibrio strains in the marine environment.