Mussels are among the most studied marine organisms because of their ecological role, economic importance and long-standing use in coastal pollution biomonitoring. Despite the bulk of data derived from traditional investigation areas, only limited knowledge is available on mussel genes and their expression in ordinary or stressing conditions. We present here the first data obtained by production and sequencing of 3' end-specific expressed sequence tags (3'ESTs) from multiple tissues of putatively unstressed mussels (Mytilus galloprovincialis). A total of 524 clusters (98 virtual consensuses and 426 singletons) derived from 829 reliable 3'ESTs were searched in the non-redundant (nr) sequence databases (National Centre for Biotechnology Information (Bethesda, USA), NCBI). Most contigs (59%) showed poor or no similarity, thus revealing unknown mussel genes, other contigs recognized some of the few available records of M. galloprovincialis (e.g. actin, cytochrome oxidase III and twitchin) and a number of significant similarities with mitochondrial (mt) or nuclear genes from other organisms were found. Actually, a variety of ribosomal as well as motility- and adhesion-related genes and some genes potentially involved in stress responses (e.g. myticin A, heat shock proteins, methallothionein) were putatively identified. Uniquely, mitochondrial transcripts were primarily represented by a cluster of 123 3'ESTs (1296 base pairs (bp) of the mussel 16S rRNA). In our knowledge, these results provide the first systematic production and annotation of ESTs in M. galloprovincialis. They also represent the first report of a wider project, based on the strategy of 3'EST identification from normal and stressed mussels and intended to define a mussel complementary DNA (cDNA) microarray for genome-wide transcription studies.