This cell line was derived from the peripheral blood of a 1 year old male with acute monocytic leukaemia. THP-1 cells show alpha-naphtyl butyrate esterase activity, phagocytose latex particles as well as sensitized sheep erythrocytes and have the ability to restore T-lymphocyte response to Con A. When incubating with TPA or DMSO the cells can be differentiated into macrophage-like cells.