The recent discovery of the molecular structure of tumor antigens expressed by melanoma cells has contributed to the development of therapeutic strategies aimed at stimulating anti-tumor immunity. The first clinical trials in patients with cancer involved systemic administration of interleukin 2 alone or in combination with alpha-interferon or other chemotherapy agents. Objective clinical responses were observed in 15 to 25% of the patients with melanomas or renal cell cancer. In order to improve these encouraging early results, different clinical protocols are being evaluated with the goal of increasing intra-tumoral concentrations of the administered cytokines. Better optimization of methods for immunizing against specific tumor antigens naturally leads to the transition from non-specific stimulation of the human immune system to tumor antigen specific immunotherapy.