Summary. Cell lines RPMI 8226, JJN3, U266 B1, NCI-H929 (all EBV À ) and ARH77 and HS-Sultan (both EBV ) have been extensively characterized in this study. EBV À lines expressed the phenotype (CD138 À , CD19 , CD20 ) whereas EBV were (CD138 , CD19 À , CD20 À ). CD56 expression was restricted to EBV À cell lines, with the exception of U266 B1, whereas PCA-1 was strongly expressed on ®ve of the six cell lines. Only EBV cell lines bound peanut-agglutinin (PNA). However, all cell lines bound the lectin Jacalin that binds the same receptor as PNA, irrespective of the receptors sialylation status. By RT-PCR and direct sequencing of their IgH V/D/J domains, ARH77 was demonstrated to use the germline sequence VH 4 -34/dm1/JH6b, whereas no arrangement was demonstrated for RPMI 8226, suggesting IgH gene deletion or mutation. HLA class I and II antigens were detected using HLA typing on all cell lines warranting their use as suitable targets for HLA-restricted cytotoxic T cells. By sensitive RT-PCR, mRNA for IL-6, IL-6R and TNFb was found expressed in all cell lines. IL-1 mRNA expression was predominantly associated with the EBV phenotype. Although mRNA for IL-3 and GM-CSF was never detected, transcripts for c-kit ligand and, more commonly, its receptor were. Likewise GM-CSF, M-CSF and erythropoietin mRNA transcripts were detected in the majority of cell lines.