Human herpesviruses 6 (HHV-6) and 7 (HHV-7) are world wide T lymphotropic viruses recently discovered. Their transmission is essentially by salivary route. Primary infections which occurred early in infancy, respectively during the first year of life for HHV-6 and in the second or third year for HHV-7, are followed by latency for life. HHV-7 is not actually associated with a disease. HHV-6 primary infection is often asymptomatic, if not it can induce exanthem subitum. HHV-6 reactivation can be symptomatic in immunodeficient subjects. The role of HHV-6 in the arising of lymphoproliferative or auto-immune diseases, discussed for a long time, is still to elucidate. HHV-6 infection is diagnosed by serodiagnosis in case of primary infection, but in the great number of cases, it would be realized by polymerases chain reaction.