The distribution behaviour ot U (IV), Th (IV), Pa (V), Zr-Nb, Mq (VI), Te (IV) and Tc (VJI) between the chelate exchanger Chelex-100 Bnd aqueous solutions containing 5M NH3CI or NH4NO3, 2M (NH4SC4or 10−3-1M Na2co3at different hydrogen ion concentrations has been investigated. It is found that U (VI) and Th (IV) aie highly sorbed (D ⩽ 103) by the resin from 5M NH4CI solution of pH 2-7, 5M NH,4NO3solution of pH 3-7, 2M (NH4 )2 SDt, or 10 M Na2CO 3The possible use of Chelex-100 for removel of U (VI) and Th (IV) from the fission products studied is discussed.