Pretreatment of human cytomegalovirus (HCMV) with human hyperimmune globulin (CytoGam) in human embryonic lung (HEL) fibroblast culture showed successful inhibition of infectivity, and decreased extracellular viral titers and extracellular viral DNA. CytoGam prevented HCMV from inducing intracellular activation of NF-kappaB, Sp-1, and P13-K signaling pathways and the production of immediate-early (IE), early (E), and late (L) viral proteins. CytoGam neutralization of HCMV in this cell culture model prevented the earliest known signal transduction events (NF-kappaB, Sp-1, P13-K activation) after viral specific glycoproteins bind to their cognate cell membrane receptors, suggesting that this agent contains highly effective neutralizing antibodies against HCMV.