Two samples of a silica-pillared montmorillonite produced using 3-aminopropyltrimethoxy silane and an alumina-pillared montmorillonite were evaluated for the removal of Cs-137 and Sr-89 from a simulated nuclear waste solution and a simulated groundwater, and the results were compared to the parent montmorillonite and two zeolites, AW500 (chabazite) and clinoptilolite. The parent and pillared clays were characterized using x-ray powder diffraction and surface area analysis by nitrogen adsorption/desorption studies. The pillared clays exhibited d-spacings of between 17.43 and 18.32 Angstrom after calcination, and surface areas ranging from 71.3 to 264.4 m(2).g(-1). Both of the silica-pillared clays and the alumina-pillared clay exhibited excellent K(d)s for (CS)-C-137 from simulated groundwater with values of 23,650, 23,260 and 144,570 mL/g, respectively. These were far better than the K(d)s obtained by clinoptilolite and AW500 which had K(d)s Of only 14,560 and 9650 mL/g, respectively. None of the pillared clays showed a high selectivity for 89Sr from groundwater or Cs-137 from simulated alkaline tank waste.-They did, however, show a slight selectivity for 89Sr in the simulated Hanford tank wastes, but this is thought to be due to a precipitation mechanism rather than to ion exchange.