Cryopreserved, autologous stem cells collected from human marrow have been used to accelerate hematopoietic recovery following intensive radiation or chemotherapy. The harvesting of adequate numbers of bone marrow cells for purposes of hematopoietic reconstitution is a potentially morbid procedure and requires the use of general anesthesia and blood transfusion during anesthesia. The ability to accelerate hematopoietic recovery using cells collected solely from the peripheral blood would obviate the requirement for a general anesthetic and avoid the discomfort experienced by patients following the procedure. Collection of hematopoietic stem cells from the peripheral blood should involve limited morbidity and risk and be well suited to repeated application in individual cases. An increasing body of in vitro and in vivo data in animals and man suggests that this goal may soon be within reach.