OUTLINE: This is a randomized, multicenter study. Patients are randomized to one of two treatment arms. Arm I: Patients undergo mobilization chemotherapy with a regimen of the center's choice, such as either of the following: Patients receive idarubicin IV over 10 minutes, etoposide IV over 2 hours, and cytarabine IV over 2 hours on days 1-3; and filgrastim (G-CSF) subcutaneously (SC) starting day 11 and continuing until blood counts recover. OR Patients receive hydroxyurea IV daily until the neutrophil count drops below 1,000/mm3 or the platelet count drops below 20,000/mm3 followed by G-CSF SC for 3 consecutive days or until leukapheresis is complete. Following mobilization therapy, patients undergo leukapheresis within 6 months of diagnosis. Patients then undergo cytoreductive therapy consisting of oral busulfan on days -5 to -2. Autologous peripheral blood stem cells are infused on day 0. Once blood counts have recovered, patients receive interferon alfa SC 3 times a week for 8 weeks, and then daily for at least a total of 6 months or until disease progression. At the discretion of the treating physician, patients may also receive cytarabine SC once a day for 10 days each month, beginning 2 weeks after the interferon alfa therapy begins and continuing until complete cytogenetic response is achieved. Arm II: Patients receive interferon alfa SC 3 times a week for 4 weeks, and then daily for 6 months. If hematological remission is achieved after 6 months, interferon treatment is continued for at least another 6 months or until disease progression. At the discretion of the treating physician, patients may also receive cytarabine as in arm I. Quality of life is assessed at defined intervals. Patients are followed for at least 2 years.