Milk is known to provide not only excellent nutrition but also protection against infection in mammalian neonates. Whey proteins, such as immunoglobulins, lactoferrin, lysozyme and lactoperoxidase, are well known antimicrobial components in milk. Håkansson et al. (1995) demonstrated that some multimeric human α-lactalbumin derivatives induced apoptosis in immature and tumour cells. Yoo et al. (1997) found that lactoferricin, which had been isolated from peptic lactoferrin as an antimicrobial peptide, induced apoptosis in tumour and immature mammalian cells. Apoptotic cell death is considered to be an important physiological function in the development and homeostasis of multicellular organisms and to be a highly controlled means of eliminating dangerous, damaged or unnecessary cells without causing tissue damage. Therefore, these findings suggest that whey proteins may have beneficial health effects by restricting specific cell population in the body.