Adoptive transfer of host defense cells may be able to correct an otherwise defective generation of competent immune cells in patients with cancer. Ex vivo-grown cytotoxic macrophages (MAC) able to recognize and destroy tumor cells but not normal cells are effective in murine models of metastasizing tumors. After the development of large-scale technology to generate MAC in vitro from blood monocytes (MO), clinical trials in cancer patients have proven the feasibility and safety of infusing >3 x 10(9) autologous MO-derived MAC activated by interferon-gamma or lipopolysaccharide. Various modalities of adoptive immunotherapy with human MAC have been realized: routes of application used were intravenous, intraperitoneal, intrapleural, and through selective hepatic artery perfusion. In addition, MAC have been generated from MO collected after granulyte-macrophage colony-stimulating factor treatment in vivo. Biodistribution studies using 111indium-labeled cells have revealed localization of MAC to sites of bulk tumor growth on regional infusion as well as to liver metastases on systemic application. Malignant ascites disappeared in about 50% of patients after intraperitoneal treatment, yet no other evidence of therapeutic efficacy of MAC could be demonstrated. Further advances of adoptive transfer of MO-derived cells are developed with emphasis on the generation of antigen-presenting cells primed in vitro with tumor cells or specific peptides.