We have compared the lipid and apolipoprotein values and the frequency of DNA polymorphisms of the apolipoprotein B gene detected with the restriction enzymes, Xba I and Eco RI in 122 patients with coronary heart disease (CHD) and 80 control subjects. The patients with coronary heart disease (CHD) were defined by > 70% stenosis in at least one major coronary artery whereas the controls showed no signs of coronary artery narrowing at angiography. When males and females were considered separately, differences in triglyceride, total cholesterol and high density lipoprotein-cholesterol (HDL-cholesterol) between CHD and control subjects were significant only for females. The polymorphism studies showed no significant differences between the control and CHD subjects except for a difference in the frequency in the females of the Xba I polymorphism (p < 0.05). The X1 allele (absence of the restriction enzyme cutting site) occurred significantly more often in the patient group than in the controls. Individuals with the X1X2 genotype had the highest serum total cholesterol whereas those with the X1X1 genotype had the lowest HDL-cholesterol value. Generally, the associations between the Xba I and Eco RI alleles and serum lipid levels were weak and inconsistent. Furthermore, even after careful selection of disease and control groups, a useful role for restriction fragment length polymorphism studies in assessing CHD risk in individual patients was not demonstrated.