A 23-year-old man with persisting high fever developed hepatosplenomegaly, lymphadenopathy and massive pericardial effusion. Immunological examination revealed a marked elevation of anti-Epstein-Barr virus antibodies (anti-viral capsid antigens IgG-antibody 1:10,240, anti-early antigens-DR IgG-antibody 1:5,120), decreased activities of Epstein-Barr virus specific cytotoxic T lymphocytes, natural killer cells and lymphokine activated killer cells. A liver biopsy showed moderate sinusoidal lymphocytosis with punched-out lesions. These findings suggested severe chronic active Epstein-Barr virus infection syndrome. The patient was treated with recombinant human interleukin-2, but it was discontinued because of an adverse reaction. Twelve months later, he died of suspected pulmonary infection.