Live shellfish samples (120) were collected from nine littoral sites in Brittany (western France). They were screened for Listeria spp. and a count of faecal coliforms was carried out. Analysis of the results revealed Listeria spp. in 55% of samples, a much higher rate than the previous, infrequent, recorded data. Furthermore, the study demonstrated that the frequency of Listeria spp. in winter was more important than in summer (P < 0·001), and underlined a significant relationship between the occurrence of these bacteria and the concentration of faecal coliforms (P < 0·001). Finally, comparison of the official and Gen-Probe® methods revealed the limits of the standardized technique in the search for L. monocytogenes in shellfish.