It has long been known that food restriction markedly increases the length of life of rats and other laboratory rodents. It has been further shown that life-prolonging food restriction delays the occurrence or slows the progression of those diseases believed to limit the life span of the animal. However, the mechanisms responsible for this increase in longevity and for the delay in occurrence of age-associated disease are not known. Surprisingly little work hs been done on the effect of these life-prolonging dietary regimens on the many changes in physiological processes and biochemical characteristics that occur with age. Since biochemical and physiological explorations might well provide the information needed to investigate the basic mechanisms underlying these actions of food restriction, such a study was initiated in our laboratory. It was found that in most of the age-related functions studied changes were delayed or partially prevented by food restriction. Our studies provide a start in analyzing the mechanisms by which food restriction prolongs life and delays disease and it is to be anticipated that future research along this line will not only further define these mechanisms but in addition should greatly contribute to our knowledge of the aging process.