Twenty-four poor-risk patients with acute lymphoblastic leukemia received a modified regimen of carmustine, cytarabine, cyclophosphamide, and 6-thioguanine (BACT) followed by autologous bone marrow transplantation (ABMT). Nineteen patients were in second or subsequent complete remission (CR) when treated with this regimen; 3 died early, 2 died of pneumonia in CR, 11 relapsed within 3 months (median), and 3 remain in CR with no maintenance therapy 14-24 months after ABMT. Of the 5 patients with measurable disease who were treated, 3 had CR and 1 remains in CR without maintenance therapy more than 28 months after ABMT. The toxicity of this regimen was acceptable, but late pulmonary toxic effects remain a major concern. These results are poor in terms of efficacy, and new effective methods of eradicating acute lymphoblastic leukemia in patients with poor prognosis should be investigated.