BACKGROUND: The proliferation of peripheral blood stem cells among peripheral blood mononuclear cells (PBMCs) invitro remains unclear. There is no optimal marker for tracing PBMCs transplanted in vivo.OBJECTIVE: To observe the degree of PBMC proliferation in stem cell medium by EdU labeling and to explore thefeasibility of EdU-labeled peripheral blood stem cells.METHODS: New Zealand rabbit PBMCs were isolated and cultured for 1 to 5 days in stem cell medium supplementedwith EdU. The cells were observed and counted at 0, 1, 2, 3, 4 and 5 days in culture. The cells were harvested at eachtime point and stained with EdU fluorescent reagents. Then, confocal microscopy and flow cytometry were used to detectEdU-labeled cells.RESULTS AND CONCLUSION: (1) Freshly isolated rabbit PBMCs were rounded and showed clear outline. After 1 dayculture, most of the cells were suspended in the medium, spherical or round. There were also a few cell clusters andadherent cells scattered in a triangle or polygon shape; after 2 days culture, more cell debris were observed, and mostcells were round; when cultured for 3-5 days, increased cell debris, smaller cell mass and decreased cell densitysignificantly were observed. (2) With the prolongation of culture time, the cell count decreased gradually. (3) Whencultured for 1 day, EdU labeled cells in red were scattered. The number of cells marked with EdU red label increasedsignificantly at day 2 and remained unchanged after 3 days of culture. At 5 days of culture, the number of red cellsmarkedly decreased; the highest positive rate of EdU-labeled cells was (2.38±0.10)% at 2 days after culture. To conclude,these results showed that the proportion of proliferating cells in rabbit PBMCs was very low. EdU is capable of labelingproliferative cells among PBMCs.