One hundred nineteen patients with primary and 31 patients with nonprimary first-episode genital herpes were treated for ten days with 200 mg of acyclovir capsules or placebo capsules orally five times daily. Among acyclovir recipients with primary genital herpes, the median duration of viral shedding (two days), time to crusting of all lesions (seven days), time to healing of all lesions (12 days), and duration of local pain (five days) and constitutional symptoms (three days) were shorter than among placebo recipients (9, 10, 16, 7, and 6 days, respectively). Among patients with nonprimary first-episode genital herpes, oral acyclovir shortened the median duration of viral shedding but had no significant effect on the duration of lesions or symptoms. The time to first recurrence and frequency of recurrences were similar in acyclovir- and placebo-treated patients. Oral acyclovir treatment of primary first-episode genital herpes shortens the duration of viral shedding and symptoms and accelerates healing, but it does not appear to influence subsequent genital recurrences.