An histology and pathological survey on carpet-shell clam cultured in the south of Galicia (NW Spain) (Ruditapes decussatus) was carried out for a two years period (2000-2001). A temporal distribution of the potentially pathogenic agents were determined by histological analysis. In addition, stocks of molluscs reported to suffer mortalities during the studied period were also analyzed and the pathogenic burden determined. Pathogens do not follow a temporal pattern over studied period and no significant differences were detected nor on the presence nor in prevalence of these pathogens among all the analysed stocks. Therefore, no direct relationship can be established between infection by any pathogen and mortality episodes.