Two human Burkitt's lymphoma cell lines (HBL-4 and HBL-5) were established individually from two patients with small noncleaved cell lymphoma (Burkitt's type). The HBL-4 cell line is Epstein-Barr virus (EBV)-negative, and the HBL-5 cell line is EBV-positive. Cytogenetically, both cell lines had the same chromosomal translocation, t(8;14)(q24;q32) as those observed in the primary malignant cells from individual patients. Morphologic, immunophenotypic, cytogenetic, and molecular studies confirmed that both cell lines were derived from the primary lymphoma cells in vivo. HBL-4 cells lacked CD23(H107), CD11a(LFA-1), and latent membrane protein (LMP) but expressed CD54(ICAM-1) at low levels, whereas HBL-5 cells showed the high level of expression of CD54 and faint expression of LMP but lacked CD11a. In addition, the EBV-positive lymphoblastoid cell line (LCL) expressed CD11a, CD23, CD54, and LMP at high levels. Therefore, an HBL-5 phenotype with expression of CD54 and LMP tends toward an LCL phenotype, and the augmentation of CD54 on the HBL-5 cells in comparison with primary lymphoma cells is likely to be upregulated by LMP, probably resulting from the EBV infection. There was little difference in the BrdUrd uptake in vivo and in vitro, doubling time, tumorigenicity, and dynamics of tumor growth in athymic nude mice between both cell lines. These findings indicate that the potentiality of cell growth and tumorigenicity of these two cell lines are unlikely to be related with EBV.