Twenty-six men and women with recurrent genital herpes maintained diaries of their symptoms and signs of infection and submitted 6,515 self-collected cultures during a one-year study of acyclovir therapy. As compared with periods before or after treatment, the mean rates of experiencing symptoms or lesions, and of shedding virus were significantly lower during treatment. Acyclovir treatment reduced the rate of symptomatic shedding from 95 positive cultures to six per 1,000 cultures, but the rate of asymptomatic shedding remained relatively constant, averaging eight per 1,000 cultures. Among the isolates of herpes simplex virus studied, there was no differences in sensitivity to acyclovir between strains recovered on or off therapy or during symptomatic or asymptomatic recurrences. The endonuclease cleavage profiles of asymptomatically shed viruses were essentially the same as those of the symptomatically shed viruses from the same individual. Chronic acyclovir therapy significantly reduced the symptoms and signs of recurrent genital herpes but did not eliminate virus shedding, nor, therefore, the possibility of disease transmission.