4-Amino-1-((2R,3S,4S,5R)-5-azido-3,4-dihydroxy-5-hydroxymethyl-tetrahydro-- furan-2-yl)-1H-pyrimidin-2-one (I:R.sup.1=R.sup.2=R.sup.3=R.sup.4=H) and prodrugs thereof are hepatitis C(HCV) polymerase inhibitors. Also disclosed are compositions and methods for inhibiting HCV and treating HCV-mediated diseases, processes for making the compounds and synthetic intermediates employed in the process.