One hundred-eighty patients are randomized to receive either brovavir or acyclovir as follows: brovavir or its matching placebo once daily and acyclovir or its matching placebo five times daily. Treatment continues for 10 days. Entry into the study must occur within 72 hours of lesion development. Patients are followed in person daily or at regular intervals during study drug administration and on days 14, 21, and 28, and then monthly by telephone for 11 months thereafter.