Cigarette smoking, body fatness and relative bodyweight did not seem to explain population differences in incidence of the disorder, but there was a tendency for incidence to be related to the prevalence of hypertension, serum cholesterol values and saturated fatty acids in the diet. There were no statistically significant relations between habitual physical activity and the incidence of coronary heart disease. There was no indication that incidence was inversely related to the incidence of any other disease.