The immunotherapy of cancer, based on eliciting or enhancing the body's own capacity to mount an effective antitumor response, has produced encouraging early results in the areas of melanoma and renal-cell carcinoma. Such treatments utilizing dendritic cells (DC), immune cells that are excellent antigen presenters, are especially promising. We performed a phase I clinical trial assessing the administration of autologous DC pulsed with HLA-A0201-specific prostate-specific membrane antigen (PSMA) for the treatment of 51 men with hormone-refractory prostate cancer. Participants were divided into five groups receiving four or five infusions of peptides alone (PSM-P1 or PSM-P2; group 1 and 2, respectively), autologous DC (group 3), or DC pulsed with PSM-P1 or P2 (group 4 and 5, respectively). No significant toxicity was observed. Immune reactivity against PSM-P2 was detected in HLA-A2+ patients infused with DC pulsed with PSM-P1 or -P2 (group 4 and 5). An average decrease in PSA was observed only in group 5. Seven partial responders were identified based on NPCP criteria + PSA. The excellent tolerance of this treatment approach, as well as the enhanced cellular responses, decreased PSA levels, and partial clinical responses in some patients suggests that it holds great potential in prostate cancer therapy.