The safety, tolerance, and clinical effects of combined therapy with recombinant interferon-α (IFN-α) and interleukin-2 (rIL-2) administered subcutaneously for 2 courses of 4 weeks each, with 4 weeks interval between courses, given as outpatient therapy have been assessed in 10 patients with Philadelphia chromosome (Ph1)-positive chronic myelogenous leukemia (CML). All patients were previously treated with conventional chemotherapy and 3 failed to respond to IFN-α administered prior to our study. Median duration of disease from diagnosis was 36 months. Seven patients were in first chronic phase and the other 3 were in blast crisis, second chronic phase, and relapse post-bone marrow transplantation (BMT), respectively. Hematological response (median follow-up 16 months) was observed in 9 patients, with a decline in number of white blood cells and platelets. Elimination of Ph1 was observed in the patient who relapsed post-BMT with complete elimination bcr/abl RNA by polymerase chain reaction. Rebound lymphocytosis and eosinophilia were observed in most of the patients. Toxicity was acceptable. The main adverse effects were fever, chills, fatigue, anorexia, nausea, and vomiting. The side effects were reversible and no interruption of treatment was required. There was no treatment-related hospitalization or deaths. These data suggest that simultaneous subcutaneous IFN-α and rIL-2 home therapy is feasible, reasonably well tolerated, and potentially beneficial in CML patients. These observations may have important implications for the treatment of minimal residual disease following allogeneic and autologous marrow transplantation.