OBJECTIVE To provide a status report on the use of interferon (IFN)-alpha in patients with chronic myelogenous leukemia (CML). METHODS Data on IFN-alpha therapy for CML collected from published articles identified in a MEDLINE computer search. RESULTS Previously untreated patients with low-risk factors and early-stage disease consistently had the best results in clinical trials. A dose response was seen, with patients treated with dosages of 5 million units (MU)/m2 per day showing the greatest incidence of cytogenetic remissions. In addition, randomized trials showed a survival advantage for IFN-alpha-treated patients. In studies comparing IFN-alpha therapy to chemotherapy, IFN-alpha produced significantly more major and durable cytogenetic responses than chemotherapy did. In studies combining IFN-alpha and chemotherapy, patients had significantly more cytogenetic responses, although more patient accrual and follow-up data are needed to offer conclusive statements concerning durability of response. IFN-alpha also showed activity in maintaining remissions after both chemotherapy and bone marrow transplantation. CONCLUSIONS IFN-alpha has significant activity in patients with CML, with best results at dosages of 5 MU/m2 per day. At these dosages, in patients with early-stage, Philadelphia+ CML, hematologic response rates of 70% to 80% and cytogenetic response rates of 50% (approximately 20% of which were complete) are seen. One randomized trial shows a survival advantage with cytogenetic response in IFN-alpha-treated patients, and this advantage appears to be unrelated to the degree of that response. These questions remain under study.