Intranuclear inclusions typical of cytomegalovirus infections were first noticed in 1881 by German scientists who thought they represented protozoa. After viruses were grown in cell cultures, Weller, Smith and Rowe independently isolated and grew CMV from man and mice in 1956-1957. Antibodies in 30-100% of normal adults indicate not only a past infection, but the presence of a present latent infection. The presence of CMV DNA in tissues and most organs surveyed indicates the ubiquity of latent infection. CMV disease requires the virus and some deficiency of immunity such as occurs in the immature fetus, in AIDS, and in transplant patients on immunosuppressive drugs. Antiviral agents can inhibit CMV replication but they cannot prevent or cure latent infections. A pharmacological approach using the many leads in understanding latency is needed.