Cytomegalovirus (CMV) is an important cause of disease in the immunocompromised patient and CMV infection is associated with predominantly mononuclear inflammatory response. Since products of the CMV immediate early (IE) gene region are potent trans-activators, we used the monocyte cell line THP-1 and a transient transfection assay to determine if these viral proteins upregulate expression of the TNF gene. The IE genes of CMV upregulated TNF gene activity as judged by increases in promoter activity, steady state mRNA, and protein production. The presence or absence of the 3' untranslated region of the TNF gene did not affect gene expression induced by the IE gene products. These studies suggest that activation of TNF gene expression by the CMV IE gene products may, in part, account for the inflammatory response associated with CMV infections.