In a prospective epidemiologic study in company employees in Westfalia aimed at improving early diagnosis of coronary heart disease in 3069 men and 1387 women, concentrations of HDL-apolipoprotein A-I and HDL-cholesterol were measured and the results were correlated with several risk factors of coronary heart disease. A negative correlation between hypertriglyceridaemia and HDL-cholesterol (r = 0.25 male;-0.27 female;p less than 0.001) and between relative body weight and HDL-cholesterol (r=-0.21 male;-0.20 female;p less than 0.001) could be shown but not between hypertriglyceridaemia and HDL-apolipoprotein A-I and between relative body weight and HDL-apolipoprotein A-I. In cigarette smokers HDL-apolipoprotein A-I as well as HDL-cholesterol were found to be lower than in non-smokers. On the other hand HDL-apolipoprotein A-I but not HDL-cholesterol was positively correlated with systolic and diastolic blood pressure.