The two autosomal codominant alleles of the Apo E‐N/D polymorphism, Apo E and Apo E(1, have a considerable influence on plasma lipid levels and distribution in man.Serum cholesterol levels are highest in phenotype Apo E‐N, intermediate in phenotype Apo E‐ND, and low in phenotype Apo E‐D. Contrary VLDL‐cholesterol is highest in phenotype Apo E‐D, intermediate in heterozygotes, and lowest in phenotype Apo E‐N. Serum‐triglyceride, VLDL‐triglyceride and the ratio of VLDL‐cholesteroI/serum‐triglyceride are also intermediate in phenotype Apo E‐ND between the two opposite homozygous groups. 10 % of heterozygous Apo E‐ND subjects exhibited a β‐VLDL subfraction compared to 0.8 % in phenotype Apo E‐N and 100%in Apo E‐D.Hence the three phenotypic groups exhibit metabolic differencesin vivo, and the gene Apo E'l has a mild dyslipoproteincmic effect even in a single dose. The Apo E‐N/D polymorphism may therefore be a major influence on the occurrence of arteri