Organochlorine compounds, such as polychlorinated biphenyls (PCBs) and DDT compounds (DDTs), are important components of the chemical pollutants found in all parts of the marine environment. They are potentially hazardous to living systems because of their inclination to bioaccumulate in the lipid component of biological species and their resistance to degradation. Prolonged exposure to these pollutants can interfere with normal physiology and biochemistry of the marine organisms. It is, in fact, well-known that these compounds exhibit a broad range of toxicological responses, including immunotoxicity, reproductive deficits, teratogenicity, endocrine toxicity and carcinogenity/tumor promotion (Ahlborg et al., 1994). The occurrence and severity of the toxic effects depend on various factors, such as the level of pollutants in the organism, the susceptibility of the species and the duration of exposure. In the last decade, particular emphasis has been placed upon the toxicity of some PCB congeners, the so-called ‘‘coplanar’’ or ‘‘dioxin-like’’ PCBs, which may adapt a planar conformation and activate the aryl hydrocarbon (Ah) receptor. These compounds are thought to share a common mode of toxic action with dioxin (2,3,7,8-tetrachlorodibenzo-p-dioxin,TCDD), the most toxic member of the planar chlorinated hydrocarbons. There is an extensive amount of literature reporting the levels of these contaminants in marine organisms occupying higher trophic levels, such as dolphins (Watanabe et al., 2000; Storelli and Marcotrigiano, 2000a), whales (Gauthier et al., 1998; Ross et al., 2000), and seals (Tarasova et al., 1997), whereas comparatively little data are available for elasmobranch fish (Serrano et al., 1997, 2000), especially from the Mediterranean Sea (Storelli and Marcotrigiano, 2001; Storelli et al., 2003a, 2004). With respect to these literature findings, this study investigated the accumulation profile of individual PCB congeners and the levels of DDTs and its metabolites in the liver of a small cartilaginous fish, Scyliorhinus canicula, from the Mediterranean Sea. In addition, 2,3,7,8-TCDD equivalency of the monoand non-ortho coplanar PCB congeners Edited by Bruce J. Richardson