The mercury concentrations in various tissues of an adult bottlenose dolphin, Tursiops truncatus, were determined by nameless atomic absorption spectrophotometry. Mercury was concentrated in the kidneys and liver at levels in excess of 18 parts per million (dry weight basis). One sample from the right lobe of the liver contained 34.5 ppm mercury. With the exception of skin and subcutaneous tissue, a sample from the medulla oblongata and a bone sample (skull fragment), all samples run exceeded 1.0 ppm mercury. Studies as to the prevalence of high mercury levels in Tursiops truncatus and other marine mammals as well as the effects such levels have on behavior, fecundity and survival are recommended.