77 patients with a first attack of genital herpes were entered into a double-blind trial to compare the efficacy of acyclovir with that of inosine pranobex. 24 patients received acyclovir with that of inosine pranobex, and 28 both drugs. Patients treated with acyclovir or both drugs healed more quickly and had a shorter duration of viral shedding than those treated with inosine pranobex. The time to first recurrence and frequency of subsequent recurrences were similar in the three treatment groups. Acyclovir is the treatment of choice for patients with a first attack of genital herpes.