[en] High radiotoxic effects associated with Auger electrons of iodine-125 on the living systems have been reported in the literature. The extreme radiotoxicity of Auger electrons experimentally observed occurs when Auger emitter radionuclide is incorporated into the structure of DNA or taken place very close to it. The microdosimetric considerations showed that each decay of iodine-125 results one dsb on the DNA helix. Of course, this leads to die the cell. On the other hand, it is also known from the literature that the normal and cancer cells have some times high level activities of some kind of hydrolytic enzymes. These enzymatic activities can lead to the selective accumulation of some specific toxic aglycones into the nucleus. For example, the toxic aglycones of glucuronide compounds such as aniline-mustard, β-naphthol, 8-hydroxy-quinoline, etc. have the selective incorporation potential into the nucleus of living cells having high level of β-glucuronidase activity, e.g. RIF and spindle-shaped sarcoma tumors. Starting from this enzymatic activities and consequently the selective accumulation of some kind of glucuronide compounds, iodine-125 as an effective Auger electron emitter, and iodine-131 as a scintigraphic agent will be able to be selectively incorporated into the nucleus of cancer cells having high level of β-glucuronidase activity. In this study, β-naphtyl-glucuronide was extracted from the urine of a rabbit treated with β-naphthol, and the purified product was radioiodinated using iodogen method. The preliminary scintigraphic tests showed that this compound was rapidly accumulated in kidneys reaching up to the maximum level about 10 min after the injection, and very quickly transferred into the bladder. (author)