Natural leukocyte interferon and recombinant interferon alpha-2 have effected remission rates between 10 and 20% in the treatment of multiple myeloma. Response rates have been higher in untreated patients than in relapsing or primarily refractory cases. Patients with slowly proliferating tumors, early tumor stage or IgA-monoclonal protein seem to show increased sensibility to interferon as compared to patients without those characteristics. First trials using combined interferon chemotherapy regimens suggest that the toxicity associated with this treatment modality remains acceptable. At present, however, one cannot definitely decide whether and to which degree the combination therapy will improve the response rates.