Because dendritic cells (DC) are central to the induction of antigen-specific T cell responses, their use for the active immunotherapy of malignancies has been of considerable interest. Since clinical trials with DC-based vaccines have been initiated, a number of important developmental issues have become apparent. These include the ideal source and type of DC, the form of antigen and method of loading DC, whether to induce maturation, the route and timing of immunization, and the optimal clinical scenario. Clinical responses such as stability of disease and tumor regressions have been reported in some patients, particularly with melanoma, myeloma, and prostate cancer.