The field of hematopoietic stem cell transplantation is rapidly evolving. Realization that hematopoietic stem cells give rise to the immune compartment has resulted in clinical trials of hematopoietic stem cell transplantation for patients with autoimmune diseases. Allogeneic hematopoietic transplants are a form of adoptive immunotherapy resulting in beneficial graft versus tumor effects. Large numbers of hematopoietic cells can be collected with ease. Therefore, a renewable source of cells for ex vivo genetic manipulations is readily available. Multiple trials combining hematopoietic transplants and gene therapy are in progress. One such application is the infusion of allogeneic lymphocytes containing a suicide gene to abort graft versus host disease. Hematopoietic stem cell transplantation is in reality the clinical and practical application of cellular therapy. Hematopoietic transplant physicians are by design or by practical application evolving into cell and gene therapy specialists. The excitement and enthusiasm in hematopoietic transplantation is that it offers a door to the future. A future not of drugs or titrating poisonous chemotherapy but rather of cellular and gene therapy. 1 ALLOGENEIC PERIPHERAL BLOOD STEM CELL TRANSPLANTATION FOR HEMATOLOGIC DISEASES Martin Korbling University o/Texas MD. Anderson Cancer Center, Houston, Texas 77030 INTRODUCTION Circulating hematopoietic stem cells have emerged as an alternative to bone marrow (BM) stem cells for allografting. For many years the reconstitutive potential of circulating stem cells was questioned; peripheral blood stem cells (PBSC) were even characterized a waste product (1).