Histochemical distribution and quantification of trace metals (copper-Cu-, zinc-Zn- and iron-Fe-) were studied in oyster, Crassostrea angulata heart (auricle and ventricle) from different southwest Spanish coasts. In green Crassostrea angulata specimens (green coloration in gills and visceral mass), numerous brown cells (blackish-brown) were observed in the wall of the auricles and dispersed by connective tissue, where inflammatory lesions related with granular amoebocytes were observed. However, only a few brown cells (translucent ligh-brown) were detected in auricles of normal oysters. Histochemically, Fe, Cu and Zn granules were observed in the wall of the heart (auricles), in brown cells, as well as in the granular amoebocytes, which are increased in green Crassostrea specimens. Auricle brown cells reacted weakly with PAS and Alcian Blue techniques. These cells contain proteins, as well as cysteine and cystine groups; these residues (-SH and S-S) being very abundant in the heart of green specimens, specially in brown cells and in granular amoebocytes. Lipofuscin granules were detected in these brown cells and in granular amoebocytes. On the other hand, in the heart (normal and green specimens), Zn levels were higher than Fe and Cu concentrations and heavy metals analyzed were lower in heart of normal than in green specimens. In green specimens, Cu and Zn levels were higher in auricles than in ventricles.