Purpose: Peripheral blood stem cell mobilization using growth factors is a common method of stem cell collection for transplantation, however, little is reported concerning safety of continued growth factor delivery in exceptional responders with very high white blood cell (WBC) counts in preparation for pheresis. We performed a retrospective study of the safety of growth factor delivery for leukapheresis in those with WBC counts greater than 60,000/µl. Methods: Allogeneic donors received 5 days of granulocyte colony-stimulating factor (G-CSF) at a daily dose of 10 or 16 µg/kg. Autologous donors received G-CSF 10 µg/kg/day +/− chemotherapy until peripheral blood CD34+count reached 10/µl. Granulocyte donors received 300 µg dose of G-CSF the day prior to donation. Results: Out of 3,037 leukapheresis collections from 1998 to 2005, we identified 303 collections from 204 donors or patients who had a WBC > 60,000/µl. WBC counts were ≥100,000/µl in seven of these subjects. If inadequate stem cell dose was obtained with pheresis with WBC counts this high, patients had growth factor dosing decreased 50% but still received a dose till stem cell collection was completed. Of the 204 subjects, 122 were patients and 82 were donors. These 204 donors/patients had no serious adverse events reported other than the common reports of myalgia, bone pain, and headache associated with administration of growth factors. Pain levels ranged from mild to severe and usually were managed by over the counter analgesics. Conclusions: Continuing ½ the dose of neupogen to complete the pheresis process appears safe in subjects with very high white blood counts. J. Clin. Apheresis 30:28–31, 2015. © 2014 Wiley Periodicals, Inc.