Background: Transplantation of hematopoietic progenitor cells is widely used to ameliorate the consequences of bone marrow failure. In allogeneic transplantation, peripheral blood progenitor cells (PBPCs) from an HLAmatched donor are collected by apheresis and then identified using flow cytometric methods as being CD34 marker positive cells. Case Report: A 25-year-old healthy male was matched with an obese 106 kg 23-year-old female diagnosed with acute lymphoblastic lymphoma. After a routine course of G-CSF induction, a 2-day PBPC collection procedure with a collection volume of 12 L/day was planned. All samples for CD34 estimation were shipped, stored, and tested according to the laboratory standard regulations. Testing was performed per International Society for Hematotherapy and Graft protocol, and CD341 cells were immunophenotyped using monoclonal antibody against CD34 and CD45 by multicolor flow cytometry. Results: The cumulative yield of both collections was 70.6 3 10 6 CD341 cells (0.67 3 10 6 CD341 cells/kg), which fell short of the requested dose of 530 3 10 6 (5 3 10 6 CD341 cells/kg). Surprisingly, the recipient engrafted successfully and 12 days posttransplant short tandem repeat testing demonstrated only T cells of donor origin in the peripheral blood. Conclusion: To our knowledge, no successful engraftment has been reported as yet with such a poor collection of PBPC. The amount of transfused CD341 cells (0.67 3 10 6 /kg) was significantly less than the minimum required amount (5 3 10 6 /kg).