1. The turnover of plasma esterified cholesterol was measured in normal and hyperlipidaemic subjects during diets rich in either carbohydrate, polyunsaturated fat or saturated fat. Turnover was measured from the rate of incorporation of radioactive mevalonic acid into plasma esterified cholesterol.
2. The turnover of esterified cholesterol was greater with polyunsaturated than with saturated fat in each of four normal subjects.
3. In sixteen studies carried out with carbohydrate-rich diets, plasma esterified cholesterol turnover tended to increase as the cholesterol concentration rose. Turnover appeared also to be higher among subjects with carbohydrate-induced hyperlipidaemia especially when they were overweight. Thus, esterified cholesterol turnover was significantly correlated with the plasma concentrations of both cholesterol and triglyceride and with body weight.
4. The physiological function of esterified cholesterol is not known but these findings suggest that it may be related to lipid transport.