Forty-five patients suffering from advanced B-CLL were randomized to receive interferon-alpha (IFN alpha) or no treatment after achieving complete remission or partial response, following a chemotherapy protocol called MiNa. The two groups were fully comparable in terms of clinical characteristics and level of response obtained by chemotherapy. IFN alpha was given at a dose of 3 megaunits three times a week intramuscularly for 1 year. The IFN-treated patient group showed a significantly longer duration of response and a less frequent incidence of infections as compared to the no treatment group. A minority of patients who had had partial response to chemotherapy obtained complete remission while on therapy with IFN alpha. Toxicity was mild and patient compliance was excellent. We conclude that IFN alpha may have a role as maintenance therapy in CLL for patients responding to chemotherapy.