This paper presents the progress of an ongoing study within Working Group N°27 of the CETAMA[1] regarding the performances of software used for determining the isotopic composition of plutonium and uranium, by means of γ spectrometry, in the presence of “disturbing” radioactive emitters and of various matrices. The “disturbing” radio-emitters are some minor actinides (242Am, 243Am, 237Np, 243Cm etc.), fission products (137Cs, 125Sb, 154Eu etc.) and/or activation products (60Co etc.). All these radionuclides can be found in waste from the nuclear industry. Matrices can also vary (metal, vinyl…). In some instances, these radionuclides and matrices are in high enough quantities to disturb the analysis by the software for determining the isotopic composition. This paper presents the outline and first achievements of this. [1] The CETAMA (Commission d'Etablissement des Méthodes d'Analyse), part of the CEA, has served laboratories for analysis and monitoring facilities throughout the French nuclear sector. Working group N°27 brings together experts in neutron and gamma spectrometry measurements to identify suitable non destructive assay methods for waste packages of all shapes, all backgrounds and all levels of alpha or beta-gamma emitters.