Dendritic cells (DCs) are professional antigen‐presenting cells (APCs) that can be used for vaccination purposes, to induce a specific T‐cell response in vivo against melanoma‐associated antigens. We have shown that the sequential use of early‐acting hematopoietic growth factors, stem cell factor, IL‐3 and IL‐6, followed by differentiation with IL‐4 and granulocyte‐macrophage colony‐stimulating factor allows the in vitro generation of large numbers of immature DCs from CD34⁺ peripheral blood progenitor cells. Maturation to interdigitating DCs could specifically be induced within 24 hr by addition of TNF‐α. Here, we report on a phase I clinical vaccination trial in melanoma patients using peptide‐pulsed DCs. Fourteen HLA‐A1⁺ or HLA‐A2⁺ patients received at least 4 i.v. infusions of 5 × 10⁶ to 5 × 10⁷ DCs pulsed with a pool of peptides including either MAGE‐1, MAGE‐3 (HLA‐A1) or Melan‐A, gp100, tyrosinase (HLA‐A2), depending on the HLA haplotype. A total of 83 vaccinations were performed. Clinical side effects were mild and consisted of low‐grade fever (WHO grade I–II). Clinical and immunological responses consisted of anti‐tumor responses in 2 patients, increased melanoma peptide‐specific delayed‐type hypersensitivity reactions in 4 patients, significant expansion of Melan‐A‐ and gp100‐specific cytotoxic T lymphocytes in the peripheral blood lymphocytes of 1 patient after vaccination and development of vitiligo in another HLA‐A2⁺ patient. Our data indicate that the vaccination of peptide‐pulsed DCs is capable of inducing clinical and systemic tumor‐specific immune responses without provoking major side effects. Int. J. Cancer 86:385–392, 2000. © 2000 Wiley‐Liss, Inc.