A simple density-cut separation technique is described for obtaining GM-CFC concentrates from the peripheral blood of patients with chronic granulocytic leukemia (CGL) for autografting at the acute blastic phase of the disease. Large numbers of granulomonocytic colony forming cells (GM-CFC) were recovered from a single procedure (68.4 X 10(6) GM-CFC). The cryopreservation of these concentrates in liquid nitrogen allowed the recovery of 46.6 +/- 33.8% viable GM-CFC. An improved yield of GM-CFC was obtained by avoiding washing the cells (65.2 +/- 41.1%). The separation technique resulted in a concentrated suspension of progenitors in a small volume of medium (mean = 15 ml) allowing a great reduction in the amount of the cryoprotective agent injected into the patient at autografting. Preliminary data obtained in 4 patients transfused in blastic crisis after chemotherapy, with or without TBI, indicated the capacity of stored concentrates to repopulate these patients.