10 patients with advanced non-Hodgkin's lymphoma of low malignancy were treated with partially purified HulFN-beta. They received daily i.v. infusions of 4.5 X 10(6) IU for 4 weeks, followed by 9 X 10(6) IU daily for 2 weeks. Patients with stable disease during this period received consolidation therapy with 4.5 X 10(6) IU three times per week for a maximum of 20 weeks. Six out of 10 patients had progressive disease after the initial 6 week treatment and 4 had stable disease. Two of the latter developed progressive disease during consolidation therapy, one had a complete remission of minimal bone marrow involvement, and one was in partial remission with a loss of bone marrow infiltration but unchanged lymph node enlargement.