The length and stable secondary structure of RNA mol. are general obstacles in RNA synthesis because of current technol. bottlenecks. A simple and cost effective process for large-scale preparation and purification of long oligoribonucleotides with stable secondary structure was presented. High homogeneous RNAs are transcribed in vitro with T7 RNA polymerase using linear 2'-Ome modified DNA templates, which were prepared by primer extension instead of PCR amplification or linearized plasmid DNA transcription to reduce contamination. The crude transcripts are then directly subjected to an anion-exchange HPLC using source 15Q to sep. T7 RNA polymerase, unincorporated rNTPs, small abortive transcripts, endotoxin and DNA templates from pure RNA products. The novel process does neither require tedious phenol/chloroform extraction nor denaturation of RNA, which is especially useful for larger RNAs preparations