ABSTRACT. Despite the great commercial and economic importance of mussels, Mytilus galloprovincialis (Bivalvia, Mollusca) in Greece, little information is available concerning their population genetic structure. We used RAPD markers to examine genetic differentiation and potential impact of aquaculture practices and other anthropogenic activities on the genetic structure of two cultivated and eight wild mussel populations collected from one Turkish and nine Greek coast sites. Five random decamer primers were chosen, among 34 tested, for the analysis of 433 individuals. Eighty-eight bands (genetic loci) were scored, all of which were polymorphic. No indication of reduced genetic variability was observed in the cultured populations. In contrast, a loss in genetic diversity was observed in populations from two localities (Canakkale and Kalochori) that are heavily polluted by chemical contaminants. analyses and exact tests revealed significant heterogeneity among M. galloprovincialis population samples, although their genetic divergence seemed to be independent of geographic distances. Anthropogenic activities, i.e., marine pollution and transplantation of mussels, appear to have played an important role in shaping patterns of genetic diversity and differentiation among Greek M. galloprovincialis populations.