An adenovirus type-2 was isolated from peripheral blood lymphocytes and throat washings from a patient with severe chronic active Epstein-Barr virus infection. Despite the Epstein-Barr virus reactivation, attempts to establish spontaneous lymphoblastoid cell lines from peripheral blood lymphocytes and to immortalize cord lymphocytes with throat washings were unsuccessful due to a marked cytopathic effect. The supernatants from the cultures induced cytopathic effect in cultured cord lymphocytes, MRC-5 cells, A-549 cells, or Vero cells. Virus particles with adenovirus morphology were seen by electron microscopy. Using type-specific antisera, the isolate was identified as adenovirus type-2. In addition, both Epstein-Barr virus and adenovirus type-2 genomes were seen in the colonic tissues and spleen. These results suggest that the combination of Epstein-Barr virus and adenovirus type-2 may be etiologic agents in the development of chronic active Epstein-Barr virus infection in this patient.