The preparation of fully protected diisopropylamino-β-cyanoethyl ribonucleoside phosphoramidites with regioisomeric purity>99.95%is described. It is demonstrated that the combination of standard DNA protecting groups, 5′-O-DMT,N-Bz (Ade and Cyt),N-/Bu (Gua),β-cyanoethyl for phosphate, in conjunction with TBDMS for 2′-hydroxyl protection, constitutes a reliable method for the preparation of fully active RNA. Average stepwise coupling yields in excess of 99%were achieved with these synthons on standard DNA synthesizers. Two steps completely deprotect the oligoribonucleotide and workup is reduced to a fifteen minute procedure. Further, it is shown that the deprotected oligoribonucleotides are free from 5′-2′linkages. This methodology was applied to the chemical synthesis of a 24-mer microhelix, a 35-mer minihelix and two halves of a catalytic‘Hammerhead Ribozyme’. These oligoribonucleotides were directly compared in two distinct biochemical assays with enzymatically (T7 RNA polymerase) prepared oligoribonucleotides and shown to possess equal or be