Fly ash from a fluidized-bed coal combustor was neutron-activated and administered to male Fischer 344 rats by a single nose-only inhalation exposure. The activated fly ash contained 46Sc and smaller amounts of other gamma-emitting radionuclides. Whole-body clearance of radioactivity to 127 d was described by an exponential equation, with the long-term component having a biological half-life of 78 d. High-resolution gamma spectra of the lungs were obtained with a Ge(Li) detector and the relative activities of several fly ash constituents were compared. The activities of 152Eu, 134Cs, 54Mn, and 60Co significantly decreased with time relative to those of 46Sc and 59Fe. These results indicate that the clearance of fly ash is similar to that of other relatively insoluble particles and that some elements may have been preferentially dissolved from the fly ash particles in vivo.