Thirty patients randomized to the Acyclovir (ACV) group (26 with dendritic lesions, 4 geographic lesions) and 34 patients randomized to the idoxuridine (IDU) treatment group (26 dendritic lesions, 8 geographic lesions) with epithelial herpetic keratitis were evaluated for efficacy and adverse reactions in a multi-center, double-masked, randomized, stratified trial. Patients were treated with either 3% acyclovir ophthalmic ointment or 0.5% idoxuridine ophthalmic ointment five times a day for 14 days. The results of the trial indicated no significant difference between ACV and IDU as antiviral agents in the treatment of epithelial herpetic keratitis. The overall healing patterns of ACV and IDU adjusted for lesion type and prognostic factors, including presenting condition (initial or recurrent disease), duration of symptoms, prior ophthalmic steroid use, and positive pretreatment herpesvirus culture, as well as, the healing patterns within each lesion type adjusted for these factors, were not significantly different between the two treatment groups. There was no significant difference between the two groups in the frequency of development of deeper involvement. The only significant difference (P less than 0.01) in the frequency of development of adverse reactions was found in the incidence of development of superficial punctate epitheliopathy (IDU-42%, ACV-11%).