Inferferon alfa-2b (IFN) plays a major role in the current management of previously untreated patients with chronic myelogenous leukemia (CML) as well as patients with CML who have relapsed after bone marrow transplantation. Hydroxyurea (HU) is the best conventional drug for treatment of CML in the chronic phase. Ten patients, six men and four women, 40-70 years of age, were treated during the accelerated phase of CML with a combination of IFN and HU. Patients had received only HU during the chronic phase of the disease. All patients were positive for the Philadelphia chromosome and had an excess number of blasts in peripheral blood smears (more than 10%), as well as increased numbers of basophils and eosinophils but a low leukocyte level of alkaline phosphatase. Eight of them had splenomegaly. Five patients (50%) survived for 1-3 years, achieving complete hematological remission. Three patients had a partial hematological response and died within 1-2 years. Two patients with aggressive disease died within 3 months of the blastic crisis. It appears that combination therapy with IFN and HU might be a useful alternative for patients in the acclerated phase of CML who have failed to respond to HU alone.