Our objective is to find methods of manipulating the diet of an individual, as opposed to the population, in order to reduce the risk of neoplasia. The work proposed is based on the following observations: When non-inbred rats are given freedom of dietary choice, the quantity and composition of the diet selected varies from animal to animal in a way that greatly increases the risk to the individual of developing a neoplasm. This effect occurs regardless of the quantity and composition of the diet selected. The individual specificity in dietary conditions that favor oncogenic processes suggests that among conventionally fed animals, those that develop tumors under one set of conditions would have been less predisposed to do so if they had been maintained under different dietary conditions. The proposed studies have been designed to establish whether or not knowledge of each individual's "optimal" tumor-promoting diet can be used to decrease the risk of spontaneous neoplasia by dietary manipulations, and, to what extent genetic factors determine the optimal tumor-promoting diet of each individual. The dietary preference exhibited by an animal early in postweaning life characterizes the dietary habits throughout much of the animal's lifetime. This therefore offers a basis for the selection of the dietary regimen to be imposed for regulating tumor susceptibility. For maximizing tumor risk, a diet similar to that selected by the individual under free-choice conditions will be provided. For reducing tumor risk, the diet to be provided will differ from the one selected by that individual under free-choice conditions. BIBLIOGRAPHIC REFERENCES: Ross, M. H. Symposium: Role of Nutrition in Aging; Chairman's Introductory Remarks. Proc. 9th Internat. Congr. Nutrition, Mexico City 1: 351-352 (1975). Ross, M. H. Nutrition and Longevity in Experimental Animals. In Nutrition and Aging, pp. 43-57 edited by M. Winnick, J. Wiley & Sons, Inc. (1976).