The determination of rhenium in molybdene is achieved by thermal neutron activation. Rhenium is separated by an extraction in basic medium followed by an ion-exchange in thiocyanate medium. This method gives a detection limit of 1.5x10$sup -9$g after an irradiation of 20 mn in a neutron flux of 4x10$sup 12$cm$sup -2$xs$sup -1$. (FR)