Autologous bone marrow transplantation represents a new approach to the treatment of malignant diseases when conventional therapy has failed. For this reason, the authors have collected bone marrow from 46 patients, including 24 with acute leukaemia, 7 with chronic myeloid leukaemia, 10 with lymphosarcoma and 5 with solid tumours. The mean of total cryopreserved CFU-c was 8.5 X 10(6) (range: 0.2-25). Ten cases of autologous bone marrow transplantation are reported. Seven patients had been prepared with high dosage chemotherapy alone (TACC) and three with chemotherapy combined with total body irradiation. Haematopoiesis restarted within 9 to 15 days in 5 patients and within 22 to 34 days in the other 5. Complete remission was obtained in all 5 patients with acute myeloid leukaemia grafted during their first relapse, the longest remission up to now being 390 days. One patient with chronic granulocytic leukaemia is still in second chronic phase after 360 days. Stem cells were transplanted early in the course of a T-lymphosarcoma, during complete remission; maintenance chemotherapy was withdrawn, and the chances of success of this treatment alone are being evaluated. The kinetics of blood and bone marrow CFU-c populations after transplantation were studied in 4 cases and were found to correlate closely with haematopoietic recovery following ablative bone marrow therapy. Stem cell transplantation can only be justified in acute leukaemia if it is carried out immediately after complete remission to consolidate the results and, hopefully, to prolong the remission.