This invention has as one of its aspects a method to provide a safe an effective treatment for synovectomy. The method involves the administration a material to the affected joint, allowing the material to localize in the synovial membrane, and then applying an external stimulus that interacts with the material to provide therapy. The materials of this invention are preferably particles, which are either magnetic or contain a heavy element. The external stimuli of this invention includes an alternating magnetic field to heat magnetic particles, infrared laser to heat heavy elements, or electromagnetic ionizing radiation (X- or gamma-radiation) that interacts with heavy elements to produce a localized radiation dose.