Ten patients with acute lymphocytic leukaemia (ALL) and four patients with acute undifferentiated leukaemia (AUL) in relapse or refractory to conventional therapy were treated with remission induction therapy consisting of an anthracycline antibiotic and cytosine arabinoside. Twelve patients had previously demonstrated resistance to vincristine-prednisone and nine patients had prior anthracycline therapy. Nine patients achieved complete remission after one course of therapy with a median time to remission of 30 d. Of five nonresponders, three died of sepsis with marrow hypocellularity and no evidence of residual leukaemia. Only two patients had unequivocal evidence for resistance to an anthracycline-cytosine arabinoside regimen. Myelosuppression and infection were the most significant complications of therapy. The data presented indicate that marrow ablative chemotherapy with an anthracycline antibiotic and cytosine arabinoside is an effective regimen for remission induction in adults with ALL and AUL refractory to vincristine-prednisone. The use of these agents in remission consolidation therapy may offer the possibility of providing a reduction in residual resistant cells that are present after successful remission induction therapy with conventional agents.