The modulatory effects of caloric intake on the rate and extent of both spontaneous and induced disease incidence is well known, but the significance of these effects in the interpretation of testing data has only recently become appreciated. This is especially true relative to the impact of caloric intake on both survival and background incidence for common tumors. In order to enhance the health and survival of animals ongoing chronic toxicity testing it has been suggested that such tests should restrict food consumption. Although this restriction will result in increasing survival of the test animals, it may also effect the expression of toxicity by altering agent metabolism and disease progression. Focus in this symposium is on the necessity to control dietary consumption in toxicity tests (dietary control), and if such a need does exist to what level of consumption should be diet be focused (caloric restriction).