Levels of Hg, Cd, Cr and Pb were determined in several marine organisms collected on the Castellón coast during 1986 and 1987. Different tissues were analyzed in order to know the degree of accumulation of heavy metals; soft tissues of Mytilus galloprovincialis (Lamarck, 1819), and Carcinus mediterraneus (Czeniarsky, 1884), and muscle, digestive tract (except liver), liver, gills, kidney and gonads of Sardina pilchardus (Walbaum, 1792), Mullus surmuletus (Linnaeus, 1758), Mullus barbatus (Linnaeus, 1758), and Thunnus thynnus (Linnaeus, 1758). Metal levels found in fish muscle, and in the soft tissues of crustaceans and molluscs, were in general not high except for mercury, particularly in M. barbatus and C. mediterraneus. However, an important accumulation of metals was found in digestive tract, liver, and particularly in kidney, as well as in gills for lead and chromium. This work is part of the Mediterranean Pollution and Research Monitoring Programme (MEDPOL), of the United Nations Environment Programme (UNEP) in its Mediterranean Action Plan (MAP).