Differences in in vitro growth characteristics between Epstein-Barr virus (EBV) genome-negative and genome-positive lymphoblastoid cell lines and between EBV genome-negative and genome-positive epithelial cell lines were investigated. All EBV genome-positive cells were able to grow in medium containing only 0.75 % fetal calf serum (FCS), whereas no EBV genone-negative cells were able to grow at this low concentration. However, there was no clear difference between the growth of the two EBV genome-negative lymphoblastoid cell lines (BJAB and Ramos) and two EBV genome-positive BJAB and Ramos sublines (BJAB/B95–8 and Ramos/B95–8) in medium containing more than 2.5% FCS. On the other hand, an EBV genome-positive clone of A2L/AH epithelial hybrid cells (cl-1) grew in both concentrations of FCS better than an EBV genome-negative clone of A2L/AH cells (cl-654). In addition, there was a difference in EBV induction between EBV genome-positive lymphoblastoid (BJAB/B95-8 and Ramos/B95-8) and epithelial (cl-1) cells after treatment with 12-O-tetradecanoylphorbol-l 3-acetate (TPA). Treatment of BJAB/B95-8 and Ramos/B95-8 cells with TPA induced a low percentage of EBV-induced early antigen but not viral capsid antigen, whereas treatment of cl-1 cells with TPA induced both early antigen and viral capsid anti