Difficulties in confirming the diet-heart hypothesis across existing literature may arise for several reasons: methodological problems inherent in estimating nutrient intake; difficulties associated with characterizing a behavior as complex as food purchasing; wide intraindividual variation in nutrient intake that make single day estimates of nutrient intake difficult to interpret; dissimilarities among dietary data collection techniques; varying lengths of followup for the observation of outcome variables in longitudinal epidemiologic studies; differing methods of lipid measurement or the lack of lipoprotein subfractionation. The Framingham data provide a unique opportunity to test the diet-heart hypothesis both cross-sectionally and longitudinally, to develop models for studying diet and heart disease relationships, and to establish the importance of dietary variables in atherogenesis and the morbidity and mortality of heart disease.