Various 3'-deoxy-3'-C-(hydroxymethyl)-, 3'-deoxy-3'-C-(fluoromethyl)-, 3'-deoxy-3'-C-(azidomethyl)-, and 3'-deoxy-3'-C-(aminomethyl)-substituted nucleosides (total 12 compounds) have been synthesized and evaluated against L1210, P388, S-180, and CCRF-CEM cells and HSV-1, HSV-2, and HIV-1 in culture. Only 3'-deoxy-3'-C-(hydroxymethyl)thymidine (36) was found to show significant anticancer activity against L1210, P388, S-180, and CCRF-CEM cells with ED50 values of 50, 5, 10, and 1 microM, respectively. None of these compounds demonstrated significant antiviral activity against HSV-1, HSV-2, or HIV-1. These compounds were also evaluated against thymidine kinases derived from HSV-I (strain KOS), HSV-2 (strain 333), and mammalian (K562) cells. The thymidine kinase (HSV-1 strain KOS) was inhibited significantly by both 3'-deoxy-3'-C-(hydroxymethyl)- and 3'-deoxy-3'-C-(fluoromethyl)thymidine.