Epstein-Barr virus is associated with several human malignancies including Burkitt's lymphoma, nasopharyngeal carcinoma, and Hodgkin's disease (HD). To examine the effect of Epstein-Barr virus nuclear antigen 1 (EBNA-1) in the pathogenesis of HD, we transfected the gene into the HD cell line L428. EBNA-1 expression was associated with significantly enhanced CD25 expression (interleukin 2 [IL-2]-receptor alpha chain) in transient and stably transfected L428 cells but did not affect the expression of IL-2 receptor beta and gamma chains. There was no up-regulation of the B-cell activation molecules CD23, CD30, CD39, CD40, CD44, CD71, and CD54 (intercellular adhesion molecule 1) or enhanced production of IL-6, IL-10, lymphotoxin alpha, and the soluble form of CD25. Stable EBNA-1-expressing L428 cells were nontumorigenic in SCID mice but showed enhanced lymphoma development in nonobese diabetic-SCID mice compared to mock-transfected cells.