The chemical composition of the otoliths of the sea bass has been determined, and special reference made to possible chemical variations during their lifespan. Differences between the organic composition of the otoliths of juvenile and adult fish were found, and included the protein contents and the aminoacid composition. Aragonite, the crystalline component was found in all the age groups studied. The aminoacid composition of the sea bass otoliths seems to indicate that the organic matrix could have different roles depending on the time of its formation.