A biomonitoring study using "Mytilus galloprovincialis" mussels was carried out, to estimate their possible employment as "natural indicators" of coastal bacterial pollution. The research was conducted from September 2001 to May 2002, twice in a month, near two coastal zones of Salento. We analysed both natural and cultivated mussels. The latter were placed in cages, after checking their starting level of microbiological pollution. The bacteriological analyses conducted simultaneously on mussels and their ambient water, were directed to the search of: total and faecal coliforms, faecal streptococci, Escherichia coli, Salmonella spp., Staphylococcus aureus and yeasts. In this preliminary study the mussels proved to be "sensitive indicators of faecal pollution", since they had an accumulation of the faecal indicators even if the water was not contaminated. Nevertheless a lower frequency in finding yeasts in the mussels (53.8%) in comparison with water (74.3%), the irregular presence of Salmonella spp. in water (3.75%) and its absence in bivalves, show the need of further studies, also through "in vitro" tests, in order to verify absorption/elimination kinetics of microorganisms.