Serum total cholesterol (TC), high-density lipoprotein (HDL) cholesterol, and HDL/TC ratios have been established in 7 188 males and females aged 15-64 years who participated in the 1979 Coronary Risk Factor Study (CORIS) baseline survey in the southwestern Cape. TC levels in a sample of 575 1- and 2-year-olds were also determined. TC levels were found to be considerably higher at all ages than corresponding values found in recent surveys in the USA. By fitting epidemiological values associated with a low risk of coronary heart disease (CHD) to the CORIS data, cut-off points (CPs) for 'desirable' TC and HDL levels and HDL/TC ratios were obtained. The CPs for TC are considerably lower than those commonly used by pathology laboratories, and their adoption would result in a greater proportion of the 'westernized' population being regarded as being at risk of CHD, and therefore as requiring diet modification or drug treatment. Experience with the diagnosis of familial hypercholesterolaemia (FH) suggests that the CORIS 80th percentile for TC will correctly identify over 90% of cases of FH. On the basis of this, TC CPs for population screening for FH are also presented.