【】Objective Observation of depletion of GFP-positive cells by diphtheria toxin in Lyz2-IRES-DTREGFP mice in vivo. Methods Transgenic mice of 6-8 weeks of age and wild-type mice of the same genetic background were randomly selected and subjected to intraperitoneal injection of 25 ng diphtheria toxin for three consecutive days, after which myeloid cell depletion was observed at different time points by flow cytometry (FCM). The combination of GFP and CD11b was used as a marker of myeloid cells (macrophages and neutrophils). Cells from bone marrow, peripheral blood and spleen were taken after intraperitoneal injection and subjected to FCM to determine the pattern of GFP-positive cells over time after diphtheria toxin injection. Results GFP-positive cells in peripheral blood decreased significantly on the third day after diphtheria toxin injection, and GFP-positive cells in spleen and bone marrow decreased significantly on the first day after injection, after which GFP-positive cells began to recover gradually. Conclusion Diphtheria toxin has a depleting effect on GFP-positive cells in Lyz2-IRES-DTREGFP mice in vivo, and the time of depletion varies at different sites.