Recombinant tumor necrosis factor alpha (rTNF alpha) has potent antitumor activity in experimental studies on human tumor xenografts. However, in humans, the administration of rTNF alpha is hampered by severe systemic side effects. The maximum tolerated dose ranges from 350 to 500 mg/m2, which is at least 10-fold less than the effective dose in animals. Isolated perfusion of the limbs (ILP) allows the delivery of high-dose rTNF alpha in a closed system with acceptable side effects. A protocol with a triple-drug regimen was based on the reported synergism of rTNF alpha with chemotherapy, with interferon-gamma, and with hyperthermia. In patients with melanoma-in-transit metastases (stage IIIA or AB), we obtained a 91% complete response rate compared with 52% after ILP with melphalan alone. In unresectable soft tissue sarcomas, this protocol was found to produce a 50% complete response with 87.5% limb salvage, since most tumors became removable. Release of nanograms levels of TNF alpha in the systemic circulation was evident, but control of this leakage and appropriate intensive care resulted in acceptable toxicity. Angiographic, immunohistological, and immunological studies suggest that the efficacy of this protocol is due to a dual targeting: rTNF alpha activates and electively lyses the tumor endothelial cells, while melphalan is mainly cytotoxic to the tumor cells. ILP with rTNF alpha appears to be a useful model for studying the biochemotherapy of cancer in man.