Solid phase synthesis of phosphonate-modified oligoribonucleotides using 2′-O-benzoyloxymethoxymethyl protected monomers is presented in both 3′→5′ and 5′→3′ directions. Hybridisation properties and enzymatic stability of oligoribonucleotides modified by regioisomeric 3′- and 5′-phosphonate linkages are evaluated. The introduction of the 5′-phosphonate units resulted in moderate destabilisation of