We have used cryopreserved autologous hematopoietic cells to repopulate bone marrow of patients receiving intensive chemotherapy and radiation. We employed the technique of density step centrifugation to concentrate stem cells from whole bone marrow. The concentrate of cells was frozen in vials using dimethyl sulphoxide (DMSO) as a cryo-protective agent and was stored in the vapor phase of liquid nitrogen. Test vials were thawed and assayed for myeloid stem cells (CFU-C) to determine the potential of the larger marrow aliquot. These test values were compared to the recovery of cells and CFU-C when the marrow was used for autotransplantation. The return of hematopoietic function after autotransplantation was evaluated and correlated with the dosage of cells and CFU-C infused.