Human fibroblast interferon(HFIF) was used in 26 patients with various malignant diseases, most of whom had previous chemotherapy. The dosages used were 3 X 10(6) IU or 6 X 10(6) IU of HFIF i. v. daily. Out of 24 evaluable patients, there were 2 partial remissions (CLL 1 and multiple myeloma 1), and 7 stable diseases (multiple myeloma 2, stomach cancer 2, non-Hodgkin's lymphoma 1, CLL 1 and malignant melanoma 1). The majority of the patients experienced fever exceeding 38 degrees C and chills, which became uncommon within several days of treatment. Other side effects included myelosuppression, general malaise, anorexia, hepatic dysfunction and renal dysfunction, which were mild and tolerable.