For adoptive immunotherapy protocols using cells of the macrophage (M phi) system, well differentiated and functionally competent effector cells are required. In this presentation the generation of a large number of M phi grown in vitro from blood monocytes (mo) is reported. Mononuclear cells (MNC) were collected by cytapheresis and subsequent Ficoll centrifugation. Mean yield was 6.9 x 10(9) MNC (range from 3 x 10(9) to 1.2 x 10(10), n = 18) with a mean mo count of 22 +/- 14%. MNC were cultured at 5 x 10(6)/ml in suspension on hydrophobic Teflon foils with 2% autologous serum for 7 days with recombinant human interferon-gamma (rhIFN-gamma) being present for the last 18 h of culture. Cells were harvested and activated mo-derived M phi separated from lymphocytes by counter-current centrifugal elutriation. On average, 42% of mo cultured could be recovered as M phi, the maximal number of M phi generated being 1.7 x 10(9) with a purity of up to 96%. Mo-derived M phi appeared to be mature by their expression of maturation-associated antigens and proved to be cytotoxic to allogeneic tumor targets in vitro. They secreted large quantities of tumor necrosis factor alpha (TNF-alpha), interleukin-6 (IL-6), and granulocyte-macrophage colony stimulating factor (GM-CSF) upon stimulation with endotoxin. Using the technology described, this study revealed that large amounts of tumorcytotoxic M phi can be generated from the peripheral blood of cancer patients to be used in adoptive immunotherapy trials.