The problem of intramolecular hydrogen atom exchange in the OsH3(BH4)(PR(3))(2) system is examined from both theoretical and experimental points of view, through ab initio MO calculations on the OsH3(BH4)(PH3)(2) system at the MP2, MP4, and CCSD(T) computational levels and variable-temperature H-1 NMR studies on the OsH3(BH4)(PPr3)(2) complex. Three different exchange processes are fully characterized from a theoretical point of view through location of intermediates and transition states. Experimental results supporting the existence of these three different exchange processes and providing definitely its intramolecular nature are also presented.