Lactoferrin (LF) is an iron-binding protein found in milk and other secretory fluids of mammals as well as in secondary granules of neutrophils. Receptors for LF were detected and isolated on activated T and B cells, monocytes, intestinal brush border cells, platelets and neoplastic cells. Very low physiologic serum levels of LF increase significantly upon infection. Serum concentration of LF is also elevated in rheumatoid patients. It is suggested that the ability of LF to bind an excess of Fe() ions, needed for growth of microorganisms and tumors, represents an important defence mechanism in humans. LF, in addition, may contribute to the protection against pathogens and their metabolites by enhancing phagocytosis, cell adherence and controlling release of proinflammatory cytokines such as IL-1, IL-6 and TNF-alpha. The protein diminishes also damaging effects of free radical release. LF possesses interesting immunotropic properties with regard to immature T and B cells by promoting phenotypic and functional maturation of these cells. LF also controls the effector phase of cellular immune response and inhibits manifestations of autoimmune response in mice. One molecular form of LF with a ribonuclease activity may have a prognostic value in breast cancer. Lactoferrin may be potentially applied in neutropenic patients or in patients with bleeding disorders as a preoperative immunomodulator.