Carbon-cesium distances are measured in the supramolecular inclusion guest-host system [Cs(p-tert-butylcalix[4]arene -H)(MeCN)] by C-13-Cs-133 REDOR NMR to illustrate the utility of solid-state NMR for the structural characterization of metal ions trapped by organic host compounds. e structural picture of the complex is obtained and the NMR-determined structure is compared to the structure obtained previously by X-ray diffraction methods. Cesium cation was chosen for study because of the importance of removing its radionucleotide from waste products. The results will show that the Cs-133 nucleus has suitable properties for REDOR NMR. It is also shown that C-13-D-2 REDOR experiments may be used as a tool to aid in C-13 spectral assignments for host compounds having hydroxyl groups, especially when there is difficulty in making the assignments. Data are also provided which show that the three remaining phenolic protons in the complex are in rapid exchange between the four phenolic sites of the calixarene.