Abstract: In this paper a radioanalytical method for substoichiometric multielement group separation is studied and applied to reactor neutron activation analysis. Zinc diethyldithiocar-bamate Zn (DDC)2 is used as the chelating agent. By a single extraction gold is separated quantitatively, and copper substoichiometricaly at the same time, while sodium is not extracted and remains in aqueous phase. These' elements are separated from 2N H2SO4 and 0.1 N HC1O4 medium. This separation method is applied to the activation analysis of biological materials. Copper and gold are separated from interfering elements with high activity (principally 24Na) and determined accurately with high sensibility. The method proves very suitable for the determination of copper, sodium and gold, the principal toxic elements in the semiconductor.