Induction of specific anti-tumor immunity by active immunization has been the aim of researchers for decades. However, a generally applicable successful immunization strategy that could be used in the clinic has not yet been devised. Recent research has been directed at identifying and defining tumor-specific and tumor-associated antigens. Several good candidates are now at hand. If these antigens are to perform optimally at immunization, there is a need for proper adjuvants. This article focuses on one adjuvant, the cytokine granulocyte-macrophage colony-stimulating factor (GM-CSF), and the possible application of this molecule to active specific immunotherapy.