The objectives of the present study were to investigate whether interferon alpha (IFN) maintenance could prolong response duration and survival in patients with multiple myeloma (MM) in objective response and to analyze the characteristics of relapse and subsequent survival. From January 1991 to November 1994, 92 patients from the Spanish Cooperative Group PETHEMA with MM in objective response after 12 courses of VCMP/VBAP chemotherapy were randomized to receive IFN maintenance vs no treatment until relapse. Prognostic factors at diagnosis were similar in both groups. IFN was administered at a starting dose of 3 mU/m2 three times per week. The IFN toxicity was moderate with granulocytopenia and fatigue being the most common adverse effects. Median duration of response from randomization until relapse was 13 months in the IFN group vs 7.7 months in the no treatment arm (P = 0.042). Median survival from randomization was 38.8 months for patients given IFN vs 32.7 months for those allocated to the no treatment arm (P = 0.12). Features at relapse were similar in patients who received IFN maintenance and in those assigned to no treatment. Finally, survival from relapse was identical in both groups. In summary, our results show a significant prolongation of response in patients maintained with IFN with no significant influence on survival. In addition, in our series features at relapse and subsequent outcome were similar in both groups.