The susceptibility of hematopoietic progenitor cells to infection by human cytomegalovirus (HCMV) was investigated using several strains of HCMV, including the recombinant strain RC256. RC256 is derived from the laboratory strain Towne and contains the Escherichia coli LacZ gene coding for beta-galactosidase (beta-gal) regulated by an early HCMV promoter. Expression of LacZ allowed the detection of HCMV in individual hematopoietic cells. Clonogeneic bone marrow (BM) progenitors, including CD34+ cells, could be infected with HCMV and would then form normal hematopoietic colonies. By polymerase chain reaction (PCR) amplification of DNA, HCMV could be detected in both erythroid and myeloid colonies. LacZ activity was observed predominantly in cells of myelomonocytic lineage. When cells derived from HCMV-infected progenitors were cocultivated with permissive human fibroblasts, infectious virus expressing LacZ was recovered. Although no characteristic HCMV cytopathology was observed in BM colonies, high virus to cell ratios resulted in a moderate inhibition of colony formation. Since infected hematopoietic progenitors can harbor HCMV for weeks and through several differentiation steps in culture, we postulate that in vivo these cells may serve as a reservoir of latent virus and contribute to HCMV dissemination.