Various cytokines can be used in the treatment of solid tumours. They are factors of proliferation and/or differentiation of haematopoiesis or immunopoiesis, and they stimulate the effector cells of anti-tumoral response. The various steps in the preclinical and clinical development of a cytokine in the field of oncology are detailed, taking IL-2 as an example. The results of the clinical trials reported (essentially with INF and IL-2) are presented and discussed.