Using mass spectrometry (MS) combined with sequence database searching, 6 of the most prominent differentially expressed proteins were analysed. Of these, 1was identified as being Heat-shock Pro tein 10, and 2 were shown to be cytoskeleton-associated proteins, myosin and actin. Heat-shock Protein 10, which is known to be involved in cellular transport and chaperoning and associated with stress situations, was more highly expressed in intertidal mussels living in littoral areas than in cultured mussels. These findings are discussed in connection with the molecular changes involved in the adaptation of mussels to different ecological conditions