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The "modified triester" and phosphodichloridite procedures for oligoribonucleotide synthesis, using 2'- silylated nucleosides, were compared. Phosphodichloridite reagents were faster and more efficient than the arylsulphonyl reagents for both dinucleotide and mononucleotide phosphotriester synthesis. / The trichloroethyl group was better than tribromoethyl, p-nitrophenethyl or methyl protecting groups for solution-phase synthesis. Trichloroethyl dichlorophosphite was used in block condensations to prepare CCCGA and UCAUAA. / An automated RNA synthesizer was developed. Nucleoside methyl chlorophosphites were used with silica gel supports. Polystyrene, polyacryloylmorpholide and controlled pore glass supports were also used but were not as satisfactory. Oligoribonucleotides, up to 17 units long, were rapidly prepared in high overall yield. The sequences were purified by TLC and gel electrophoresis. Enzymatic degradations and HPLC confirmed the composition of the products.