Vitamins, either as coenzymes or hormone-like substances play an important role in the expression of genetic information and in the regulation of cellular metabolism, differentiation, and maturation. Recent epidemiologic evidence suggests that certain forms of cancer are more prevalent among populations with a limited intake of certain nutrients. Other evidence indicates that localized deficiency of a nutrient can occur in hormone-sensitive cells without overt systemic manifestations of deficiency disease. Folic acid, because of its key role in nucleic acid biosynthesis, and vitamin A, because of its role in epithelial maintenance are of particular interest. The recognition of folate-dependent fragile sites on chromosomes suggests that folate and related compounds may play a role in preventing tumor-specific chromosome translocations and the insertion of viral oncogenes. Improved understanding of the role of nutrients in cellular maturation could provide clues for primary cancer prevention and better methods of treatment.