Epidemiologic and metabolic data are consanant with the hypothesis thata metabolic imbalance in regard to zinc and copper ia a major factor in the etiology of coronary heart disease. This metabolic imbalance is either a relative or an absoulte deficincey of copper characterized by a high ratio of zinc to copper. The imbalance results in hypercholesterolemia and increased mortaility die to coronary heart disease. The imbalance can occur due to the amounts of zince and copper in human food, to lack of protective substances in food or drinking water and to alterations in physiological status that produce adverse changes in the distribution of zinc and copper in certain important organs. Because no other agent, with the possible exception of cholesterol, has been related so closely to tisk, the ratio of zinc to copper may be the preponderant factor in the etiology of coronary heart disease.