Thehuman internal dosimetry of the radionuclidic impurities of samarium-153 in a new bone-seeking radiopharmaceutical, 153Sm-1,4,7,10tetraazacyclododecanetetramethylenephosponic acid (153Sm-DOTMP), has been estimated from preclinical data. The effective dose from the impurities in lower-specific-activity 153Sm is less than 17% of the effective dose from pure Sm-153. It has a background-equivalent radiation time for a dosage of 37 MBq/kg of less than one-half year. • The dosimetry of 153Sm-DOTMP using four sources of 153Sm with different amounts of radionuclidic impurities was assessed. • The effective dose from only the impurities in lower-specific-activity 153Sm is less than 17% of that from pure 153Sm. [ABSTRACT FROM AUTHOR]