The bioaccumulation of selected heavy metals and radionuclides ((241)Am, (109)Cd, (57)Co, (51)Cr, (134)Cs, (54)Mn and (65)Zn) from seawater was experimentally compared in the Chondrichthyan Scyliorhinus canicula (spotted dogfish) and the Actinopterygian Teleost Psetta maxima (turbot), of comparable size, age and benthic feeding habits. The speciation of these elements in seawater (salinity 38 per thousand, pH 8.1, temperature 16.5 degrees C) was also calculated to determine their potential bioavailability. The uptake rates, measured over 14 days, varied greatly among isotopes and between species. Concentration factors (CFs) in P. maxima varied 5-fold between ca. 0.2 for (51)Cr and 2.5 for (65)Zn and (134)Cs, whereas in S. canicula they varied by a much greater factor of 350, with CFs for (51)Cr and (241)Am ranging from ca. 0.4 to 140, respectively. With the exception of (134)Cs, all radiotracers were accumulated at a faster rate in S. canicula than in P. maxima, particularly for (241)Am and (65)Zn where the CFs attained during the uptake phase were, two and one order of magnitude greater in S. canicula, respectively. In contrast, (134)Cs reached a CF of about 2.5 in P. maxima, which was 5-fold greater than in S. canicula. Patterns of loss from the experimental depuration phase over 29 days showed greater similarities between species, compared to the uptake phase that highlighted the greater differences between elements. The distributions of these seven radioisotopes among six body components indicated that between the two species the skin of the dogfish displayed a greater bioaccumulation potential, particularly for (241)Am, (57)Co and (65)Zn. However (65)Zn was also distinctive from (241)Am and (57)Co in its pattern of bioaccumulation in dogfish, with its other body components attaining concentrations of (65)Zn that were comparable to the levels found in its skin. The heightened uptake of (134)Cs in turbot was characterised by a more even percentage distribution among its tissues compared to (241)Am and (57)Co, but every tissue of turbot had a higher concentration of (134)Cs, compared to dogfish, particularly the muscle and liver. The elevated uptake rates and higher CFs for most radioisotopes indicate that S. canicula is more susceptible than P. maxima to exposure and contamination by these metals and radionuclides in seawater. These experimentally-determined differences between dogfish and turbot in their bioaccumulation characteristics were assessed against a set of criteria erected to evaluate the working hypothesis that they were taxonomically based. The outcomes of this initial assessment were supportive of this hypothesis that warrants further investigation.