In order to determine whether any primary human blood cells have the ability to replicate poliovirus (PV), peripheral blood cell components were isolated and analyzed for their cell surface expression of the poliovirus receptor (PVR). Following two-color immunfluoresence staining with lineage-specific markers, the cells were analyzed by flow-cytometric methods. PVR cell surface expression was detected on most mononuclear cells expressing CD14, a marker for mononuclear phagocytes. There was no PVR cell surface expression on platelets and extremely low levels on polymorphonuclear leukocytes. Mononuclear leukocytes from Ficoll density centrifugation were found to support PV replication. The finding of PVR on mononuclear phagocytes and the ability of primary human blood cells to support PV replication in the absence of cultivation has implications for both the normal and pathogenic role of PVR.