Ion exchange on a potassium-exchanged natural zeolite at various temperatures is examined. The ions studied were cesium and cobalt, and the contact temperatures were 25, 60, and 100°C. The main focus of the work was to examine the use of natural zeolite as a direct means for the removal of radioactive contaminants. It was found that cesium was more selectively sorbed than cobalt and that higher amounts of both cations were taken up as the temperature of contact increased. The raw data could be correlated using a Brunauer-Emmett-Teller-type isotherm. The ion exchange equilibrium constants and activity of the sorbing ion on the zeolite were used in correlating the data. An Arrhenius behavior was suggested.