The last 10 years have been an exciting time for virology research, with the discovery of three new members of the Herpesviridae family. Although infection with HHV-6 and HHV-7 appears to be ubiquitous and generally mild, the full range of clinical manifestations of infection with these agents is not understood fully yet. Much remains to be learned about the newest member of the Herpesviridae family, HHV-8. Experiments designed to study the seroepidemiology of infection and routes of transmission likely will have to await the isolation of the agent in tissue culture, as well as the complete molecular cloning of the genome. Insights derived from research with HHV-8 will increase our understanding of HIV-associated disease, the role of viruses in the pathogenesis of malignancy, and potential interactions between viruses that may trigger neoplastic transformation.