Vidarabine is the first drug to become generally available in the USA for parenteral treatment of life-threatening or debilitating herpes simplex virus infections of man. For the past decade laboratory and clinical studies have been in progress to assess the pharmacology of the compound, its mechanism of action and its potential usefulness in clinical investigations. Currently, clinical usefulness has been established for herpes simplex infections of the eye and brain. Further studies in progress are evaluating the drug's ability to prevent progressive disease from herpes zoster in the immunocompromised patient, reduce mortality and morbidity from neonatal herpes simplex virus infection and improve outcome of chronic hepatitis B infection.