Intravenous acyclovir had a significant effect on the resolution of the skin rash in patients with acute zoster, but the 5-day course of therapy was not, in itself, sufficient to treat coexisting ocular involvement. In an open study, topical acyclovir was found to control herpes zoster kerato-uveitis, without recurrences and in a shorter time than if steroids alone were used. The use of steroids in combination with acyclovir led to prolonged treatment and high recurrence rates. A comparative trial of topical acyclovir versus steroids in the treatment of acute herpes zoster kerato-uveitis showed significant differences in favour of acyclovir in terms of the time to resolution of corneal epithelial disease, total treatment duration and the numbers of patients having a recurrence of infection. The reductions in treatment duration and recurrence rate would be expected to result in a reduced incidence of ocular damage and visual loss in acyclovir treated patients.