The dicesium salt of the icosahedral borane anion dodeca hydroxy-closo-dodecaborate (2-), closo-Cs2B12(OH)(12), Cs(2)4, was prepared using an improved synthetic pathway. Heating cesium dodecahydro-closo-dodecaborate, closo-Cs2B12H12, Cs(2)1, with 30% hydrogen peroxide added in successive increments at 105-110 degreesC provided Cs(2)4 in 95% yield. Reaction progress was monitored using H-1-decoupled B-11 NMR while O-17 NMR provides the most reliable way to detect the presence of peroxides in the reaction solution. The reaction may be safely increased in scale to afford Cs(2)4 in multigram quantities.