EBV is the etiologic agent of infectious mononucleosis. It is also associated with different malignancies and other diseases including emophagocytic syndrome, a severe disorder in which erithrocytes are phagocytated by macrophages and B cells. Moreover, EBV has been postulated to be involved in the pathogenesis of multiple sclerosis. We investigated the ability of EBV to infect a monocytic human cell line (THP-1) in vitro and the effects of virus growth on the monocytic immune functions. The EBV chronically infected B cell line B95.8, stimulated with phorbol and butyrrate, was used as a source of virus. The growth of EBV on THP-1 virus was documented by IFA for viral antigens and quantification of viral DNA by RealTime PCR TaqMan. EBV infected THP-1 disclosed augmented phagocytosis of Candida albicans as assessed by a phagocytosis assay performed with a double fluorescence staining which allows to distinguish internalized fungi from those not ingested. Moreover, EBV infected THP-1 also displayed an increased ability to kill cells of a human oligodendrocytes line (MO3.1). Clones of chronically infected THP-1 cells have been obtained which are presently being characterized.Our results, showing alteration of monocytic immune functions induced by EBVinfection, support a pathogenetic role of this virus in emophagocytic syndrome and in multiple sclerosis.