HCMV infection can evoke the broad spectrum of symptoms, which may be caused by the infection of responsible cell types. It is important to identify the cell types to be infected and replicated with HCMV infection for characterizing the property of HCMV infection and symptoms. Bone marrow stroma consists of heterogeneous cells, which have many cellular functions. This study was performed to verify the infectivity of HCMV to osteoblasts using the osteogenic sarcoma cell line, Saos-2, and the effect of HCMV infection to them on the cellular function. Immediate-early antigens, IE1 and IE2, were detected from 1 day postinfection (d.p.i.), and early (ppUL44) and late (gB) antigen were detected from 2 d.p.i. by the immunoperoxidase staining. All the antigens were expressed as far as observed (9 days). It was found that the virus titer in the culture supernatant and the cell pellet were 150 to 2,200 pfu/ml and 50 to 800 pfu/ml, respectively, after 4 days when the cells were infected with 2 m.o.i. Alkaline phosphatase production in Saos-2 cells infected with the different amount of HCMV was decreased to 8 to 15%, 31 to 47%, and 11 to 52% on 4, 6, and 11 d.p.i., respectively, as compared with mock-infected cells. This result suggested that HCMV could replicate in some bone marrow stromal cells and disturb the cellular function such as production of alkaline phosphatase.