The three years since our last conference in San Francisco have again seen a dramatic expansion of the number of antivirals either licensed or in the late stages of clinical trials. d4T is now licensed for HIV infection, famciclovir and the oral pro-drug of acyclovir, valacyclovir, are now licensed for VZV infections in some countries. Moreover. oral ganciclovir, cidofovir, and sorivudine are not far behind. Clinical trials with the second-site reverse transcriptase inhibitors and the protease inhibitors for HlV infection are proceeding rapidly and on a broad scale, and the preliminary results would suggest that several of these classes of drugs will be licensed as well. Despite this optimism, however, there is increasing evidence that antiviral-resistant strains of pathogenic viruses will be a significant problem, perhaps especially with therapy of HIV infection, and there remains a desperate need for improved drugs (with either improved efficacy or decreased toxicity, or both) for CMV and HIV infections. This book is the edited proceedings of the Fourth Triennial Conference on Antiviral Chemotherapy, held in San Francisco, in November 1994. The conference was sponsored by the University of California, San Francisco, and co-sponsored by the International Society for Antiviral Research (ISAR), the Macfarlane Burnet Centre for Medical Research in Melbourne, Australia, and the Australian National Centre for HIV Virology Research. The conference had been organized to present an overview of the field of antiviral chemotherapy.