Two new radiopharmaceuticals, 186Re-1-hydroxyethylidenediphosphonate (186Re-HEDP) and 153Sm-ethylenediaminetetramethylenephosphonate (153Sm-EDTMP), have been proposed as palliative treatments for metastatic bone cancer. Biolocalization properties of these chelates in animals as well as the physical decay and production properties of the respective radionuclides are consistent with those of a therapeutic agent. Subtherapeutic doses of both agents have been administered to human cancer patients to determine their biokinetics and skeletal localization. The 186Re-HEDP studies were conducted at the University of Cincinnati while the 153Sm-EDTMP studies were conducted at the University of Missouri-Columbia. The pharmacokinetics of these agents in humans were consistent with those found in animals. Imaging studies show that the retained activity localizes primarily in the skeleton with high selective uptake in skeletal lesions; there is no visualization of other organs or soft tissue. This paper will review the development and preparation procedures for these radiopharmaceuticals and briefly summarize the animal and patient data.