Dendritic cells are among the most efficient antigen-presenting cells of our immune system and they play a crucial role in immunity reactions such as the activation of T and B cells and the induction or maintenance of tolerance. New culture methods allow us to generate dendritic cells in sufficient numbers for further studies and for the preparation of antigen-loaded dendritic cells for clinical application in cancer patients. In animal studies immunization with antigen-loaded dendritic cells offered protection from growth of injected tumour cells. In experimental clinical studies in cancer patients with e.g. metastatic renal carcinoma, melanoma and B cell lymphoma some lasting remissions were observed after administration of antigen-loaded dendritic cells. Side effects were minor. Unanswered questions on tumour vaccines with antigen-loaded dendritic cells concern specific matters, such as optimal culture methods and antigen loading, and general matters, such as dose, frequency, duration and route of administration. Also, no method is currently available by which the in vivo immune response can be measured accurately.