Labeling of RNA with site-specific fluorine atoms has become straightforward in recent years and in particular has become an integrated part of engineered functional RNA with therapeutic potential, e.g. for siRNA technologies. Here, we demonstrate that temperature-dependent one-dimensional F-19 NMR spectroscopy of oligoribonucleotides is a powerful tool to obtain direct information on the conformational behavior. The approach is particularly useful for the quantification of monomolecular vs bimolecular secondary structure equilibria.