AMD3100 induces a rapid and transient mobilization of normal hematopoietic progenitor cells and APL blasts into the peripheral blood. Syngeneic B6129F1 recipient mice were left untreated (nonleukemic) or injected intravenously with APL cells (leukemic). Twelve days after APL injection, mice were treated with a single subcutaneous dose of 5 mg/kg AMD3100. Peripheral blood samples were collected immediately before and 0.5, 1, 3, and 6 hours after AMD3100 administration. (A) Total white blood cell (WBC) counts per microliter of peripheral blood in nonleukemic mice were determined by automated counting. (B) Colony-forming units in the peripheral blood of nonleukemic mice. (C) Representative flow cytometry profiles showing mobilization of Gr1⁺CD34⁺ APL blast cells following treatment with AMD3100. (D) Total white blood cell counts per microliter of peripheral blood in leukemic mice were determined by automated counting. (E) APL blast cell counts per microliter of peripheral blood in leukemic mice were determined by automated counting and flow cytometry of Gr1⁺CD34⁺ APL blast cells. Each bar represents the mean ± SD of a single experiment, for which each sample was assayed in quadruplicate. Results are representative of 3 separate experiments. *P < .05; **P < .01; and ***P < .001.