Excessive production of the tumor necrosis factor (TNF) ligand-receptor system has been found to contribute to the severity of non-Hodgkin's lymphoma (NHL). We therefore investigated the expression of TNF, lymphotoxin alpha (LTalpha), lymphotoxin beta (LTbeta), and their receptor (p55, p75, LTbeta-R) transcripts within the tumor tissue in different NHL histological subtypes. The constitutive expression of genes coding for TNF-related ligands and receptors was found in almost all 31 NHL samples studied. Semi-quantitative reverse transcription/polymerase chain reaction and computed densitometry assays revealed that the amounts of TNF, LTalpha, p55, and LTbeta-R mRNA were higher in follicular NHL than in other histological entities. Therefore tumor cell immunopurification was performed in representative follicular NHL samples and consistent results were obtained. The pattern of LTbeta gene expression was different from that of the other molecules, indicating the existence of distinct mechanisms of gene regulation. These results indicate that the transcription of genes coding for the TNF ligand-receptor system in NHL tumor tissue is more widespread than originally thought and that the heterogeneity of their expressions might be related to histological features. The expression of TNF-related ligands and receptors in tumor tissues is likely to contribute to the clinicopathological features of lymphoid-derived malignancies.