We reviewed the human epidemiologic studies of the possible protective effect against lung cancer of various dietary constituents, including preformed vitamin A, carotene, vitamin E, selenium, and vitamin C. Beta carotene has strong potential as a protective agent, though constituents of green and yellow vegetables other than carotene may account for the reduced cancer incidence observed in many studies. Selenium also deserves attention as a potential chemopreventive nutrient, though data are limited. Data on vitamin E are sparse and inconclusive, and there is little evidence that vitamin C provides protection against human lung cancer. It is likely that cessation of cigarette smoking would have a far greater influence on reducing lung cancer incidence than any known dietary modification.