The most important method of evaluation of painful total joint prostheses is review of sequential radiographs. Because clinical failure from loosening occurs late, abnormalities of alignment, the cement-bone or cement-metal interface, the bony contour, or the integrity of the prosthetic components will be found in the vast majority of cases of clinical failure. In cases in which plain radiographs are normal or equivocal, radionuclide bone scanning with Tc-99m diphosphonate agents are useful. A diffuse increase in vascularity and in uptake of radionuclide is present in infection, while a normal scan suggests that infection or loosening is unlikely. Positive arthrograms are helpful in confirming loosening and in demonstrating abscess cavities and sinus tracts, but negative arthrograms have little significance. Asymptomatic patients with radiographic evidence of loosening should be followed with sequential roentgenograms for signs of progressive bone destruction.