Batch contact tests provided data that will be useful in cesium isotherm modeling of spherical resorcinol-formaldehyde ion exchange resin. This resin is the baseline for cesium removal from alkaline high sodium nuclear waste at the Hanford River Protection Project Waste Treatment Plant and is being considered for other applications. Batch contact work at 25 degrees C found that increasing potassium concentration in alkaline solution simulating waste unexpectedly improves cesium adsorption when cesium concentration exceeds about 0.001M. At lower cesium levels potassium competes with cesium for adsorption on the resin as expected. Additional batch work found that dimethylamine cation competes strongly with sodium adsorption with no significant reduction in cesium adsorption.