The available antiviral chemotherapeutic agents for the treatment of herpes simplex type 1 and 2 and varicella zoster virus infections are discussed in respect of their mechanism of action, clinical effects, and side effects. Although effective under experimental conditions most of the antiherpetic drugs need further evaluation of clinical efficacy in controlled trials. It is possible to reduce initial herpetic pain mainly in patients with zoster by topical application of 5% 5-iodo-2'-deoxyuridine solved in dimethylsulphoxide when treatment starts within the first 3 days of blister eruption. The postzosteric neuralgia is not influenced. A shortening of pain seems also possible in primary herpes simplex virus type 2 infection. For recurrent herpes simplex there is no proven effect on duration or frequency of recurrences with available antiherpetic drugs. The indication for antiviral chemotherapy is limited not only by the unpredictable, mainly self-limited, course of herpes simplex and zoster but also by the possible side effects of chemotherapeutic agents. Severe and life-threatening herpes disease, e.g., in immunosuppressed patients or newborns, can be defeated with vidarabin applied i.v. and, in the near future, with acyclovir.