Human herpesviruses 6 and 7 are ubiquitous herpesviruses that normally infect their hosts early in life. There are two variant groups of human herpesvirus 6 (HHV-6): variants A (HHV-6A) and B (HHV-6B). Variant A has not been unambiguously associated with a specific disease but may contribute to disease in immunocompromised patients; variant B is the major etiologic agent of roseola (roseola infantum or exanthem subitum) and other febrile illnesses of young children, and has been associated with disease in immunocompromised patients. HHV-6B is frequently present in plaque regions in the brains of multiple sclerosis patients, although an etiologic association has not been proven. Human herpesvirus 7 (HHV-7) has been associated with some cases of roseola. The clinical spectrum of these viruses remains to be completely defined. Braun et al. (1 ) recently described three clinical scenarios that might warrant the use of antivirals to treat HHV-6 infections: (1) transplant recipients with idiopathic pneumonitis (2), multiple sclerosis patients, and (3) patients with HHV-6-associated encephalitis. For HHV-7, cases of neurologic involvement during primary infection might warrant investigation (2 ).