Pillared clays were characterised by thermal analysis and small-angle X-ray scattering. They were then examined for their ability to take up137Cs and90Sr/90Y isotopes as a function of concentration and competing cations (Na+, K+, NH4+, Ca2+, Mg2+) in the concentration range 10−1 to 10−4 M. The radioisotope uptakes were quantified byKd (ml/g) measurements.