Hematopoietic progenitor cells (HPCs) mobilized to peripheral blood and collected by apheresis techniques are the primary source of grafts in adult hematopoietic stem cell transplantation. Yet 10-20% of patients fail to produce the adequate number of CD34+ cells required to proceed to high-dose therapy and transplantation. This session will focus on mechanisms of stem cell mobilization, management strategies for poor mobilizers, and approaches to optimize the collection of HPCs. Speakers will describe the science of the stem cell niche, mechanisms by which hematopoietic and stromal cells interact and modifications that lead to stem cell mobilization. Predictors of poor mobilization and options to salvage HPC collections will be discussed, including the use of chemotherapeutic, biological and novel agents. Presentations will address methods to optimize HPC-A collection yields, technical approaches to the challenges of difficult mobilization, product goals, component quality parameters and the potential effects on infusion and outcome.