6653 Background: Literature regarding the association of aging and stem cell numbers is conflicting. No compelling evidence exists that hematopoietic stem cell numbers decline with age. Early progenitor cells represent only a fraction of total CD34 cells. The ratio of CFU-GM/CD34 provides an estimate of the proportion of primitive hematopoietic stem cells in the stem cell compartment. The hypothesis is that primitive stem cell numbers decrease with age. The present study attempted to determine if a decline in stem cell reserve occurs with age in patients undergoing autologous hematopoietic stem cell transplant for various malignancies. Methods: Four hundred and thirty six patients who underwent autologous peripheral blood stem cell transplant from 10/97 to 12/02 were included in this retrospective analysis. Patient characteristics included: age, gender, race/ethnicity, ABO blood group, weight, height, body surface area; disease and treatment characteristics included: diagnosis at the time of transplant, bone marrow involvement by the tumor, number of chemotherapy regimens and h/o prior radiation; collection characteristics included: number of mononuclear cells/kg (MNC), CFU-GM/kg (Colony Forming Unit- Granulocyte Monocyte), CD34+ cells/kg and the ratio of CFU-GM/CD34. Results: The multivariate analysis demonstrated that MNC doses were associated with a significantly higher CFU-GM/CD34 ratio (p<0.0001) presumably reflecting the need to collect a greater number of MNC to reach a target CD34 cell dose for transplant in patients with lower stem cells reserves. However, no significant decrease in the ratio of CFU-GM/CD34 ratio was found with age and, in fact, patients aged 60 or more had a significantly lower ratio (p=0.01) as compared to the younger patients, indicating no general compromise in the stem cell reserve of this selected group of patients with aging. CONCLUSION: Older patients who were candidates for transplantation showed no significant decline in their stem cell reserve with aging. Individual susceptibilities and co-morbid conditions, rather than a general decline in stem cells may result in increased chemo-toxicity with aging. No significant financial relationships to disclose.