We studied 30 patients in order to evaluate the therapeutic efficacy and toxicity of alfa interferon associated with busulfan as maintenance treatment in de novo chronic granulocytic leukemia. Patients received 0.2 mg/kg of busulfan and reached complete hematological remission (CHR). Patients were then randomized in two groups: one to receive busulfan to be administered when the leukocyte count was above 15 x 10(9)/L, and another to receive subcutaneously 5 million IU of alpha-interferon three times per week (plus busulfan if the leukocyte count went above 15 x 10(9)/L). The duration of CHR was longer in the alfa-interferon group: 31 vs 16 months (p = 0.03) but no cytogenetic remissions were observed. Alfa interferon was well tolerated: no patient was excluded from the study due to toxicity.