Orally administered acyclovir has been shown to have an effect on genital herpes simplex virus infections. In primary infections, all published trials report a significantly reduced duration of viral shedding and an accelerated healing time, but the effect of the drug on the severity of clinical symptoms was less apparent. Acyclovir does not seem to prevent virus latency nor to influence subsequent genital recurrences. The treatment of recurrent infections was not reported to show as good as by primary infections. However, the drug did shorten the time of viral shedding as well as prompt the reduction of lesions. The clinical response was improved if the therapy was self-initiated by the patients and acyclovir was also reported to cause recurrent attacks to abort. No serious adverse events caused by the drug have been published. As the risk for development of viral resistance associated with prolonged or repeated administration of acyclovir is not known, it should be used with caution and primarily patients with initial herpes genitalis and in patients with painful and frequent recurrences.