A 15-year-old boy with a 13-year history of periodic fevers, lymphadenopathy, and leukocytosis showed virological, serological, immunohistologic, and molecular evidence of persistent, active, Epstein-Barr virus (EBV) infection. Acyclovir and several other agents failed to alter his clinical course. Comprehensive immunological studies could not identify a defined immune deficiency syndrome to explain the persistent infection, although he does continue to have circulating polymeric EBV-specificimmunoglobulin type A, as is seen in individuals during acute EBV infections. In vitro work suggests that this polymeric antibody prevents B cell infection by EBV. Cumulative data suggest that this patient suffers from a novel form of EBV infection.