Plerixafor can rescue the outcome of failing chemotherapy-based stem cell mobilization. However, the optimal time for plerixafor injection in this setting has not been determined. This was investigated by retrospective analysis of data from 48 mobilizations with plerixafor, chemotherapy, and granulocyte-colony stimulating factor (G-CSF). The required yield of 2.0 × 10(6) CD34+ cells/kg was collected from 71% of patients; the median total yield was 4.1 × 10(6) CD34+ cells/kg. Patients to whom plerixafor was administered late (≥ 15 days) after chemotherapy, after a long duration (≥ 13 days) of treatment with G-CSF, or when the white blood cell count was high (≥ 20 × 10(9)/L) were mobilized as efficiently as other patients. Plerixafor was shown to rescue mobilizations at a comparable rate in patients with critically low levels of peripheral blood CD34+ cells (<3/µL) and those with higher concentrations. These data suggest that late administration of plerixafor in the course of chemotherapy-based mobilization does not contribute to the failure of this strategy.