Pyrrolo-dC is a fluorescent nucleoside that codes as dC and base pairs efficiently with dG. Preliminary evidence indicates that pyrrolo-dC triphosphate is an excellent substrate for Taq, Pfu and Vent polymerases and is incorporated specifically opposite dG. Pyrrolo-dCTP has been available for some time and is in use in biological assays. Pyrrolo-CTP is a fluorescent ribonucleotide with fluorescence exquisitely sensitive to its environment and is of great interest for RNA structural research. The pyrrolo-C project is a joint development by Berry and Associates, Inc. and Glen Research Corporation.