There are primary and secondary malignant liver tumors for which principal treatment is surgical resection. There is no established treatment for unresectable malignant liver tumors, however, and the prognosis for these is quite poor. An effective treatment for malignant liver tumors is thus urgently needed. Recent advances in molecular biology have uncovered the structures and/or functions of many cytokines thought to have a strong relation with the mechanisms of the antitumor effect of biological therapies. Availability of those cytokines in large amounts and homogeneously owing to advances in recombinant technology makes it possible to use them clinically. Among cytokines demonstrating antitumor activities, tumor necrosis factor-alpha (TNF-alpha) is one of the strongest. However, severe toxicity such as hypotension, abnormalities in liver function, leukopenia, chill and thrombus formation makes TNF-alpha difficult to use systemically as an antitumor drug. To enhance cytotoxicity while decreasing the side effects, especially hypotension, we developed a mutein called TNF-SAM2 by protein-engineering. The biological activity of TNF-SAM2 was more beneficial than TNF-alpha for antitumor therapy, since its side effects were milder. In contrast, using the isolated limb perfusion (ILP) method against malignant melanoma and soft tissue sarcoma of the extremities in combination with TNF-alpha and melphalan, a high response rate of 70-100% was observed. These observations led to the re-evaluation of TNF as an antitumor drug. A preliminary clinical trial was done using TNF-alpha combined with the formation of a closed circuit (isolated hepatic perfusion method) targeting the liver and a response rate of over 75% was achieved against malignant liver tumors. To isolate the liver from the systemic circulation, however, required a laparotomy, so that patients were subjected to excessive surgical stress. Isolated hypoxic hepatic perfusion (IHHP) using balloon catheters is a treatment developed to overcome such stress and we are planning to do clinical trials of IHHP with TNF-SAM2 in combination with a chemotherapeutic agent against malignant liver tumor patients. IHHP combined with TNF-SAM2 and a chemotherapeutic agent might be more beneficial in antitumor effects as well as in maintaining good quality of life (QOL) for the patient.