Endoarterious treatment with microspheres of P32 and Cr51 cathionic resin in colloidal solution has been used by Dogliotti and his collaborators with the purpose of distributing them in the capillary arterious network of tumors and surrounding tissues. In order to study the density of distribution yielded by microspheres in the patient's body, it is suggested the use of an adequately collimated scintillating counter, utilisizing the intense Bremsstrahlung of P32 (therapeutic dose) and the gamma radiation of Cr51 (tracing dose). Different techniques, according to the extension of the radioactive distribution (as well as of the diffusing medium surrounding it) were used. The volume of the distribution has been obtained thanks to relieves on maps, realized by means of a scanner Nukab endowed with magnetic memory, the microspheres being radio-transparent. The paper shows that the introduction of radioactive microspheres, according to Dogliotti's technique, allows a rapid localization as well as a high concentration of a radionuclide into organs or into parts of organs with malignant tumors.