Syntheses of 5,6-dihydro-2-thiouridine (I), 5,6-dihydro-4-thiouridine (II), and 5,6-dihydro-2,4-dithiouridine (III) are described. The n.m.r. spectra of thio-analogues of 5,6-dihydrouridine and of their isopropylidene, p-tolylsulphonyl, triphenylmethyl, and 5′-iodo-derivatives have been reported.