The genetic variation of apolipoprotein B has been studied extensively in Finns with the aid of protein and DNA polymorphisms. Population association studies confirmed significant associations between the XbaI polymorphism of the apolipoprotein B gene and elevated serum cholesterol levels, and dietary studies suggested that the XbaI and ins/del polymorphisms might modify the serum lipid response to dietary fat intake. Studies comparing patients and controls, however, did not confirm previous studies suggesting that the multi-allelic variation at the 3'VNTR region of the apolipoprotein B gene was associated with coronary artery disease. The results suggest that the apolipoprotein B gene is involved in the regulation of serum lipid levels. A yet unknown mutation in linkage disequilibrium with the XbaI site may contribute to this regulation.