pain is the commonest clinical manifestation of bone metastases. its treatment is palliative in nature, and consists of chemotherapy, radiotherapy, hormonotherapy, diphosphonates, and drug therapy (i. e., opiates). radioactive isotopes represent an appealing alternative to conventional treatment modalities. among the different types of isotopes, wide clinical experience with 153sm has been obtained in this laboratory. in the present study, 94 patients (mean age = 65 years), who had been diagnosed of having breast, prostate and other malignant tumors, were evaluated. these patients were treated with 37 mbq/kg 153sm-edtmp. all of them complained of bone pain and had scintigraphic evidence of metastatic bone dissemination. treatment efficacy was evaluated both objectively and subjectively. eighty-five per cent (85%) of the patients reported pain relief, and analgesia was reduced by 55%. twenty-two per cent (22%) had a complete response. bone marrow toxicity was not a concern, with mild transient hematologic derangements in 30% of the patients. it was concluded that 153sm-edtmp results in relief or cessation of metastatic bone pain in a majority of patients.