As indicated in Table 1, two approaches have been taken to the development of antiviral chemotherapeutic agents. Both have met with some success although the availability of effective chemotherapeutic agents for the treatment of virus infections is very limited. This situation should change in the near future as more specific, direct inhibitors of virus replication are identified and better ways are developed for stimulating specific and nonspecific host defense mechanisms although the discussion of host defenses centered upon the interferon system, there are a variety of other nonspecific host defense mechanisms that are also important including macrophages, lymphocyte subpopulations, and other as yet poorly defined soluble mediators.