Acyclovir [9-(2-hydroxyethoxymethyl)guanine] is a new antiviral agent which has specific activity in virus-infected cells. The drug has a high therapeutic index in animal and laboratory models but had not been tested for toxicity in human eyes at the time of this study. A randomized double-blind study on patients requiring antiviral therapy for treatment or prophylaxis of herpetic ocular infections revealed minimal irritation associated with topical administration. Further controlled studies will be necessary to evaluate this compound’s clinical efficac