Thirty-nine patients with acute myeloblastic or lymphoblastic leukaemia had peripheral blood mononuclear cells collected by 3 continuous-flow leukapheresis as they entered first remission after induction chemotherapy. CFU-GM were assayed as a measure of the number of haemopoietic stem cells in each collection. Numbers of CFU-GM harvested varied among the patients (for example 0.27 to 155.10(4)/kg for ANLL patients). Nineteen patients underwent peripheral blood stem cells autografts after a conditioning regimen with high dose cyclophosphamide and TBI. The patients were transfused with a median of 2.2.10(4)/kg CFU-GM cells (0.28 to 100.10(4) CFU-GM/kg). Only 1 patient had a graft failure. The rate of haemopoietic recovery was studied for our patients and those reported in the literature. A strong correlation exists between the numbers of CFU-GM transfused and the rate of granulocytes and platelets recovery. Very rapid recovery are regularly obtained when the number of CFU-GM transfused is superior to 5.10(4)/kg.