In a double-blind, randomised trial, immune-competent adults with acute herpes zoster received either 5 mg/kg acyclovir (17) or placebo (20) intravenously three times daily. Acyclovir significantly improved rash development, as evidenced by reducing the time of new lesion formation and the times to vesicle collapse and full crusting. Pain at the end of treatment and at three months was less in the treated group but the difference was not statistically significant. Ocular involvement was not affected.