The role of alpha interferon in patients with chronic lymphocytic leukaemia (CLL) has yet to be well established. In studies carried out to date, a significantly higher response rate has been observed in previously untreated patients compared to those who have received prior chemotherapy. Patients with early-stage CLL also respond better than patients with advanced disease. Responses to alpha interferon are transient and complete responses are rare. It is not yet known whether alpha interferon can induce clonal remission, and response is usually measured in terms of the reduction in peripheral blood lymphocyte levels. In one study, a normalization of immunoglobulin levels was observed, and in another there was an increase in the absolute number of granulocytes. Further studies are needed to investigate the role of combined therapy with alpha interferon and cytotoxic agents or other cytokines, and to assess the ability of alpha interferon to prolong response duration after remission induction with chemotherapy. Toxicity is tolerable when alpha interferon is given in a low dose (e.g., 2 million units (MU)/m2 three times a week) and low doses have been shown to be as effective as high doses in CLL patients.