The combination therapy with natural type human tumor necrosis factor (n-TNF; MHR-24) and human lymphoblastoid interferon-alpha (n-IFN-alpha; MOR-22) was investigated for antitumor effect against renal cell carcinoma in a multiclinic cooperative study throughout Japan. The "Response criteria of Japan Society for Cancer Therapy" were followed for the handling of subjects and the evaluation of antitumor effect. MHR-24 was administered at a daily dosage of 5,000-10,000 JRU by intravenous drip and MOR-22 at a dosage of 5,000,000 IU daily was administered intramuscularly at the same time. Both drugs were administered for 4 weeks or longer. A total of 36 patients were enrolled as subjects in the study. None of them were classified as ineligible. Five patients, were classified as imperfectly evaluable, and 31, as evaluable for the results of treatment. The responses in the evaluable patients were partial response (PR) in 4 patients, minor response (MR) in 3 patients, no change (NC) in 14 patients and progressive disease (PD) in 10 patients, with a response rate of 12.9%. Adverse reactions to the therapy were investigated in all 36 patients. The frequent subjective and objective reactions that occurred were fever, rigors and shivering, anorexia, and generalized malaise, and the frequent abnormal laboratory findings were leukopenia, thrombocytopenia, elevation of GOT, and elevation of GPT.