This study was performed to elucidate the possible mechanism of the disturbance of hemopoiesis by HCMV infection. Saos-2 cells constitutively express mRNA of GM-CSF, and its expression was profoundly decreased by HCMV infection, which required full replication of the virus and was mediated by soluble factors released from the HCMV-infected Saos-2 cells. TGF-beta1 production was statistically and significantly increased from one day after HCMV infection. Expression and production of GM-CSF in Saos-2 cells were restored when a culture supernatant of HCMV-infected Saos-2 cells was reacted with neutralizing anti-TGF-beta antibody. Conclusively, HCMV inhibits GM-CSF expression in Saos-2 cells partly by the increased production of TGF-beta1.