Pyranosyl-RNA ("p-RNA") is an oligonucleotide system isomeric to natural RNA and composed of the very same building blocks as RNA. Its generational, chem., and informational properties are deemed to be those of an alternative nucleic acid system that could have been a candidate in Nature's evolutionary choice of the mol. basis of genetic function. We consider the study of the chem. of p-RNA as etiol. relevant in the sense that knowledge of its structural, chem., and informational properties on the chem. level offers both a perspective and ref. points for the recognition of specific structural assets of the RNA structure that made it the (supposedly) superior system among possible alternatives and, therefore, the system that became part of biol. as we know it today. The paper describes the chem. synthesis of b-D- (and -L)-ribopyranosyl-(4'->2')-oligonucleotide sequences, presents a resume of their structural and chem. properties, and cautiously discusses what we may and may not have learned from the pyranosyl isomer of RNA with respect to the conundrum of RNA's origin. [on SciFinder (R)]