Mercury exposure in dental offices may represent a health hazard. Previous studies evaluated mercury exposure through blood, urine or hair analysis. The mercury content of body fluids in hair depends on the time since mercury exposure, mode of intake and its excretion, and sequestration by different tissues. Utilizing an x‐ray fluorescence technique, the mercury burden in bone, liver, lung, spleen, and kidney was measuredin vitro. The x‐ray fluorescence, XRF, and chemical assays of the mercury content of these samples correlated. The XRF technique was used to assay the mercury content of tissues irradiatedin vivo. It was found that the mercury signal arising at a depth in tissue was reduced as the thickness of overlying material increased. Thus, the XRF assay for tissuesin vivois confined to organs near the surface. The mercury content of the superficial layers of the head and wrist were determinedin situfor a dental population. Concentrations as low as 20 μg/g could be detected with an exposure of 60 mR. Of the 298 dentists evaluated, 28% had greater than 20 μg/g of mercury in the head.