Antiviral chemotherapy has been too long perceived as being relatively impossible. Such notions adversely affect the acquisition of important specific clinical information, whereas much new knowledge is available about viral replication and cell biology which enhances the prospects for effective chemotherapy. Some immediate goals can be recognized that will further determine the ability to influence viral infections and properly interpret the drug effects. In recent controlled observations there is reason for expectant optimism, but the demonstration of antiviral chemotherapy is both disease- and host-dependent, with important nonpharmacologic aspects. Rapid specific and sensitive diagnostic tests are of paramount importance; that they can be devised is a generally accepted conclusion among virologists. Problems in the scientific evaluation of antiviral chemotherapy in man have led to the recommendations of compounds that have no proved effect; amantadine, Ara A, and interferon, however, have been shown to be efficacious. Acyclovir and bromvinyldeoxyuridine have demonstrated virus-directed chemotherapy with impressive specificity. The frontier of antiviral chemotherapy holds great promise for additional learning and improved health through the implementation of developing knowledge.