No proved case of coronary thrombosis was present among 10,267 admissions of full-blooded Navajos at the Navajo Medical Center in the years 1949-52. There were 125 cases of gallbladder disease in the same period.Questioning of 100 patients elicited that the diets of many had an average or even high amount of cholesterol in them. It was concluded that heredity is probably the most important factor in the prevention of coronary thrombosis in this select group.