An overview of all the available placebo-controlled trial data for oral acyclovir in acute herpes zoster infection has confirmed that a dose of 800 mg five times daily for seven to ten days is effective in reducing the incidence of post-herpetic neuralgia and the duration of pain. Although one study failed to demonstrate such an effect, three other studies and a combined analysis, using the log rank test, did so. The duration of pain was shortened from an average of 86 to 49 days (p less than 0.001). Future studies will need to take account of these findings since oral acyclovir is most likely to be used as the standard reference therapy.