Plerixafor is a new CXCR4 inhibitor that is able to improve peripheral blood stem cell (PBSC) mobilization when combined with granulocyte-colony-stimulating factor (G-CSF). The 'on demand' use of plerixafor at the hematopoietic recovery after chemotherapy + G-CSF may be more efficient and cost-effective, but the timing of administration and criteria for patient selection are still under investigation. We collected the data of lymphoma and myeloma patients treated with plerixafor at the hematopoietic recovery after chemotherapy + G-CSF. The decision of adding plerixafor was based on PB CD34+ cells at the time of hematopoietic recovery after chemotherapy in patients at their first or subsequent attempt, according to the attending physician choice. The primary endpoint was the assessment of the rate of patients who were able to collect >=2 x 10^6 CD34+/kg. Secondary endpoint was the assessment of the rate of patients collecting > 4 x 10^6 CD34+/kg and the median number of apheresis to reach the target.