Forty-three patients with active herpetic disciform keratitis were entered into an open study to compare the efficacy of oral acyclovir (400 mg) with acyclovir ophthalmic ointment (3%) to inhibit viral replication during treatment with 0-05% prednisolone eye drops. All patients, regardless of the mode of therapy, were treated five times a day until they were healed. The mean time to heal in the oral group was 25 9 days and in the topical group was 25 3 days. Resolution of lacrimation was significantly faster in the oral group (12.1 days versus 27-6 days). The patients on tablets also showed a greater improvement in visual acuity. No statistically significant differences were found between the two groups in the incidence of recurrences over a three-year post-treatment period. It is concluded that oral acyclovir treatment is an effective alternative to ophthalmic ointment in the management of herpetic disciform keratitis.