Total mercury concentrations (Hg_t) have been determined in liver, kidneys, skeletal muscle, melon, stomach and intestine of 35 specimens of Stenella coeruleoalba stranded on French Atlantic and Mediterranean coasts. Very high mercury levels, with concentrations reaching 80 mg Hg_t kg⁻¹ fresh weight (FW) in muscle and about 1500 mg Hg_t kg⁻¹ FW in liver tissue, were observed. Liver has the highest concentration, followed by muscle and kidney. The lowest concentrations were found in the melon. The levels observed in the Mediterranean specimens are among the highest observed in marine organisms and confirm previous reports of high mercury levels in marine mammals from the Mediterranean. Comparison between Hg_t accumulation levels in these two geographic groups of dolphins shows that Mediterranean individuals have much higher concentrations than specimens from the Atlantic. These differences provide additional confirmation for the higher Hg_t concentrations observed previously in other pelagic species (tuna, sardine, anchovy, etc.) from the Mediterranean Sea. Taking into consideration the pelagic habitat of the dolphin and the local influence of anthropogenic mercury sources it seems reasonable to assume that the main source of the high mercury concentrations observed in Mediterranean biota is natural mercury deposits located in many regions of the Mediterranean basin.