Ultrahigh-dose myeloablative antineoplastic therapy followed by autologous bone marrow transplantation (ABMT) has become an attractive therapeutic option for patients without HLA compatible bone marrow donors. Autologous bone marrow was harvested in 9 patients. In four cases the bone marrow was also treated ex vivo with a stable derivative of 4-hydroperoxycyclophosphamide, ASTA-Z 7654, to eliminate residual tumour cells. Altogether 5 patients, namely a patient with metastatic neuroblastoma, a patient with malignant histiocytosis, a patient with recurrent sacrococcygeal malignant teratoma and two patients with acute myelogenous leukaemia in first remission are in continuous remission so far from 125 + to 821 + days (median 657 + days). These patients were transplanted at the time of minimal tumour load (first remission) and in good clinical condition 3-7 months after diagnosis, while 3 of the four patients who died were transplanted in first or repeated relapse after one to several years of chemotherapy. It is concluded that the earliest possible recognition of a refractory therapeutic situation is of utmost importance for successful ABMT. Patients with an unfavourably responding neoplasm should, therefore, be already primary candidates for ABMT.