A useful synthetic methodology was developed to synthesize and radiolabel a series of (E)-5-(2-[125I]iodovinyl)uracil nucleoside substrates for herpes simplex virus type-1 thymidine kinase (HSV-1 TK). (E)-5-(2-[125I]Iodovinyl)-2'-deoxyuridine ([125I]IVDU, 10), (E)-5-(2-[125I]iodovinyl)-2'-fluoro-2'-deoxyuridine ([125I]IVFRU, 11), (E)-5-(2-[125I]iodovinyl)-2'-fluoro-2'-deoxyarabinouridine ([125I]IVFAU, 12), and (E)-5-(2-[125I]iodovinyl)arabinouridine ([125I]IVAU, 13) were synthesized in 63-83% radiochemical yield by reaction of the unprotected (E)-5-(2-(trimethylsilyl)vinyl) precursors (6-9) with [125I]ICl. Cellular uptake of these labeled compounds (10-13) was evaluated in vitro. All compounds showed minimal uptake in the KBALB cell line. However, increased uptake was observed for all compounds in KBALB-STK cells which are transduced with a replication incompetent Moloney murine leukemia virus vector encoding the HSV-1 TK gene. The results indicate that uptake of these compounds in KBALB-STK cells is variable and highly dependent on the nature of the sugar 2'-substituent. When a fluoro (12) or a hydroxy (13) substituent is present in the arabinofuranosyl (up) configuration at the 2'-position, there is diminished cellular uptake in KBALB-STK cells relative to hydrogen (10) or fluorine (11) in the ribofuranosyl (down) configuration at the 2'-position. Our results indicate that radiolabeled IVFRU (11) is most promising for further in vivo studies.