B cell type chronic lymphocytic leukaemia (B-CLL) cells carry the Epstein-Barr virus (EBV) receptor CD21 and can be infected in vitro with the virus. The infected cells exhibit an unusual EBV program, they express the nuclear proteins but not latent membrane protein 1 (LMP-1). Similar cells were encountered in lymphoid tissues of infectious mononucleosis (IM) patients and in lymphoproliferations of immunosuppressed patients. EBV infected B-CLL cells can be regarded as model for this viral program. In B cells the regulation of LMP-1 is executed mainly by EBV encoded nuclear antigen 2 (EBNA-2), interacting with several cellular proteins and these complexes bind to specific sequences in the LMP-1 promoter. ATF2 and c-Jun were shown to be among the interacting partners of EBNA-2. These molecules can be detected in experimentally infected B lymphocytes. We found c-Jun and/or phosphorylated ATF-2 (p-ATF-2) expression in some B-CLL ex vivo samples. They disappeared or their expression declined promptly in explanted cells, even if they were infected with EBV in vitro. Activation of the infected B-CLL cells by exposure to CD40L was accompanied by p-ATF-2 and c-Jun but not by LMP-1 expression. In one of three clones tested, subsequent treatment with histone deacetylase inhibitors (HDACi), TSA or n-butyrate, could induce LMP-1. Treatment with phorbol-12, 13-dibutyrate (PDB) induced LMP-1 expression in three of four clones. Neither the HDACi nor the PDB treated cells survived.