The pathogenic effects of human cytomegalovirus (CMV) infection in vitro on hematopoiesis were investigated. Normal human bone marrow cells from both seronegative and seropositive donors were challenged with CMV (Towne or wild-type strain) and tested for their responsiveness to the recombinant hematopoietic growth factors granulocyte-macrophage colony-stimulating factor (GM-CSF) and granulocyte-CSF (G-CSF), respectively. Regardless of the serostatus of the donor, infection with CMV resulted in a significant decrease in the proliferation and colony formation of hematopoietic progenitor cells in response to both growth factors, with more pronounced suppression in response to G-CSF being observed. Evaluation of the colony composition revealed a profound decrease in colonies of the granulocytic (CFU-G), or granulocyte-macrophage (CFU-GM) lineages, while suppression of multipotential (CFU-GEMM) and erythroid (BFU-E) colony-forming cells occurred after infection with wild-type but not the laboratory strain of CMV. Although no evidence of productive virus infection could be seen in colony-forming cells, in situ hybridization studies and immunohistochemical staining revealed the presence of CMV-specific mRNA and immediate-early antigens, demonstrating that a small proportion of cells were abortively infected. These studies demonstrate that CMV can infect bone marrow progenitor cells and interfere with normal hematopoiesis in vitro, which may help to explain the hematologic defects seen during acute infections with CMV in vivo.