We report the disease characteristics and therapeutic results for 25 patients suffering from essential thrombocythaemia (ET), treated with recombinant interferon-alpha-2b (IFN-alpha 2b). ET was diagnosed according to the criteria of the Polycythaemia Vera Study Group. All patients were programmed to receive a subcutaneous induction treatment consisting of 3 MU of IFN-alpha 2b daily for 6 months. In responding patients, treatment was continued for a further 6 months with 3 MU of IFN-alpha 2b three times a week. Complete response was achieved in 13 of 25 patients, partial response in 10 of 25. In 2 cases, therapy was unsuccessful. Side effects were usually mild, consisting of flu-like symptoms in most cases, and were easily controlled by paracetamol. After a median follow-up of 14 months after discontinuation of the treatment, most patients retained the therapeutic response in the absence of toxicity.