CD40 is a cell surface signalling molecule expressed on normal B-cells and B-cells malignancies. Activations of CD40 (via binding CD40 ligand, CD40L) in normal B-cells promotes B-cell survival and is vital for activation of the immune response. However, activation of CD40 can induce or prevent apoptosis in malignant B-cells. Furthermore, CD40-activating agents are entering clinical trails as cancer therapies. B-cells were isolated from over twenty Non-Hodgkin's lymphomas and non-malignant lymph nodes and the effect of CD40 ligation on apoptosis and expression of apoptosis regulators was assessed. CD40L suppressed apoptosis in all B-cell malignancies tested, accompanied by significant increases in Bcl-X_L protein expression and differential regulation of Bcl-X splicing and promoters. Mcl-1 protein expression was also regulated by CD40 stimulation. Although A20, survivin, Bfl-1 and BNIP3 (a novel CD40-target gene identified in this study) were regulated by CD40 in some samples, this was not consistent. Antisense oligonucleotides to Bcl-X_L and Mcl-1 demonstrated that these proteins were key for survival of lymphoma cells. NF-κB mediated both the pro-survival effects of CD40 and upregulation of Bcl-X_L and Mcl-1 expression. Microarrays were developed and used to characterise CD40-induced gene expression. This identified both novel CD40-target genes and also genes that were differentially regulated in cell lines with different survival outcomes to CD40 activation e.g. SLAM and SH2D1A. Therefore, CD40 acts as a potent survival signal for primary B-cell lymphomas leading to regulation of the key anti-apoptotic proteins Bcl-X_L and Mcl-1, via activation of NF-κB. This raises concerns over forthcoming clinical trails utilising CD40 activation as a treatment for cancer but suggests that targeting Bcl-X_L, Mcl-1 or NF-κB may be a useful approach for treating lymphoma.