Apolipoprotein E genotypes were measured in 83 patients with familial hypercholesterolaemia (FH) and in 175 blood donor controls. Following DNA extraction from peripheral blood, each sample was genotyped for the Apo E polymorphism by polymerase chain reaction. No significant differences were found in the levels of the epsilon 2 and epsilon 3 alleles between the two groups, while the epsilon 4 allele was approximately twice as prevalent in the FH patients as in controls (P = 0.006, df = 1). Of the FH patients, 8.4% were homozygous for the epsilon 4 allele while this genotype was rare in controls (P = 0.009, df = 1). These results suggest that the epsilon 4 allele is over represented in the FH population and may contribute to increased cholesterol levels and consequent vascular disease.