153SmEDTMP was obtained from enriched 152Sm irradiated at the 5 MW Chilean Research Reactor and labelled at a molar ratio of 15:1 pH 7.5. Biodistribution, autoradiography, radiochemical purity tests were done for evaluation. 40 patients were treated with 37-55 MBq/kg weight. Bone scans using 99mTcHMDP were obtained prior and after treatment. Bone marrow depression was observed in 37% of them and normal liver function in all of them. In 45% the pain dissapear completely, in 22.5% significantly decreased and partially in 30%. In 17 patients more than one dosis was injected. Our preliminary results indicate that 153SmEDTMP is a promising radiotherapeutic agent for palliative treatment of metastatic bone cancer pain and encourage its use specially because it can be produced in countries with low economic resources, thus a large number of patients can get the benefits of this new procedure.