We describe a new method for the solvent-free synthesis of borohydrides at room temperature and demonstrate its feasibility by the synthesis of three of the most discussed borohydrides at present: LiBH4, Mg(BH 4)2 and Ca(BH4)2. This new gas-solid mechanochemical synthesis method is based on the reaction of metal hydrides with diborane to form the corresponding borohydrides. The synthesis will facilitate the preparation of a wide range of different borohydrides, including mixed borohydride systems, with tuneable sorption properties. We propose that diborane is an intermediate compound for the hydrogen sorption in borohydrides and may be the key for a reversible hydrogen ab- and desorption reaction under moderate conditions. © 2010 the Owner Societies.