A series of acyclonucleoside and nucleoside analogues in which a hydroxy group has been replaced with a N-hydroxyureido group have been prepared and tested against a panel of Herpesviruses, Hepatitisviruses and HIV. The only noticeable activity was against VZV (Varicella zoster virus). The only promising compound was 1-(2',3'-dideoxy-3'-(N'-hydroxyureido )-β-D-erythro-pentofuranosyl)thymine (9). Its β-D-threo epimer (B) and its N'-hydroxyureido positional isomer (18) exhibited activities more than one order of magnitude lower, whereas its 5'-deoxy-5'-(N-hydroxyureido) positional isomer (A) was devoid of any activity.