During the last 10 years, the role of specific nutrients in cancer prevention and cancer treatment has been the subject of intense basic, preclinical, and clinical research. At present, the major focus of nutri- tional oncology is on the mechanisms of carcinogenesis and their modification by nutrients and on cancer prevention studies in animals and humans. Some human epidemiological studies have confirmed the hypothesis, developed on animals, that there is an inverse relation- ship between the intake andor level of 3-carotene, vitamin A vita- min E, or vitamin C and the risk of cancer, whereas others have shown no such relationship. This is not unexpected, since the protective effect of individual nutrients may be too small to be detected by epidemiological methodologies in which a single vitamin or mineral is considered as one variable. Conclusive evidence regarding the role of nutrients in human cancer prevention will come from a well- designed human intervention study using one or