Study subjects will be patients who have failed to achieve an adequate mobilization of hematopoietic progenitor cells (so-called stem cells) into their blood stream to safely proceed with hematopoietic stem cell transplantation as a component of treatment for a hematological malignancy. There are several possible chemo-mobilization procedures that a primary clinician may prescribe and when blood cell counts at the end of these procedures document an inadequate number for transplantation, there is no accepted clinical course of action other than to repeat the procedures and sometimes add another drug, such as plerixafor. This investigation is based on a single center abstract presented at a hematological meeting (the 2012 ASCO University Annual Meeting) where 7 of 9 patients previously identified as poor mobilizers achieved sufficient mobilization with addition of hyperbaric oxygen therapy to standard care (1). This project is to recapitulate the study in a somewhat larger patient population (20 subjects).