Cytokine gene therapy is a potentially powerful antineoplastic strategy. It provides paracrine cytokine secretion in the region of putative tumor antigen that maximizes antitumor immune responses and minimizes systemic toxicity. A wealth of animal experimentation has demonstrated the effectiveness of cytokine gene therapy in a variety of tumor models. Enough evidence has mounted such that human cytokine gene therapy trials are underway throughout the United States and elsewhere.