An iodinated analogue of deoxyuridine, with antiviral activity against herpes simplex virus (HSV) and potential radiosensitizing activities. Upon ocular administration, idoxuridine (IUdR) is converted to its mono-, di-, and triphosphate forms, is incorporated into DNA and disrupts viral replication. Upon oral administration of the idoxuridine prodrug ropidoxuridine and hepatic conversion by aldehyde oxidase into idoxuridine, this agent incorporates into DNA and sensitizes cells to ionizing radiation by increasing DNA strand breaks.