This subtle, worldwide microorganism is a member of the herpes virus group. It is large for a virus, contains DNA, and has a complex protein capsid. It forms latent, lifelong infections, and, except for occasional serious infections in infants and malnourished youngsters, seldom produced a disease state. With increased use of immunosuppression therapies for conditions ranging from arthritis to cancer to organ transplants, the incidence of adults with major infections of CMV increases yearly.