Tungsten accumulates in bone but is neither labile nor inert once absorbed. Tungsten?s relatively high cytosolic solubility and availability are problematic given its association with childhood lymphocytic leukemia. In light of tungsten?s technological prevalence, and the increased concern of regulatory agencies, here we characterize the chemical form and localization in mice exposed to tungsten through drinking water. Using X-ray fluorescence spectroscopy, we report accumulation of tungsten in bone tissue with some sites having ~10-fold greater intensities than background levels. The long bone tissue studied includes cortical, cancellous and bone marrow. Persistence of tungsten in cortical bone tissue following removal of the source indicates that it is retained in an insoluble form. The X-ray absorption near-edge structure spectra for tungsten in these tissues indicate that it is no longer in the originally administered form, orthotungstate, but rather resembles the heteropolytungsate species, phosphotungstate.