Enantiomerically pure (+)- and (-)-carbocyclic thymidine, (-)-carbocyclic 3'-epi-thymidine, (+)-carbocyclic 3'-deoxy-3'-azidothymidine, (+)-carbocyclic 2,3'-O-anhydrothymidine, (+)-carbocyclic 3'-O,6'-methylenethymidine, and (+)-(6'S)-carbocyclic 6'-methylthymidine were synthesized in a stereospecific manner from common chiral pools of (+)-(1R,5S)- and (-)-(1S,5R)-2-oxabicyclo[3.3.0]oct-6-en-3-one and evaluated for antiviral activity. (+)-Carbathymidine and, to a lesser extent, (+)-carbocyclic 2'-deoxyadenosine proved to be effective against HSV-1 [minimum inhibitory concentration (MIC): 0.2 and 2 micrograms/mL, respectively] and HSV-2 (MIC: 2 and 20 micrograms/mL, respectively), but virtually inactive against TK- HSV-1 (MIC: 40 and 100 micrograms/mL, respectively). (+)-Carbathymidine was also active against vaccinia virus (2 micrograms/mL). None of the compounds had a specific effect on the replication of HIV or other RNA viruses.