We have compared apolipoprotein E gene polymorphism in 91 Australian men aged 30-50 who had been referred for coronary angioplasty and in 172 healthy younger men. 5 of the 19 patients who were less than 40 years of age were homozygous for the epsilon 4 allele, representing a 16-fold increase in prevalence compared with controls. In patients aged 40-50 the epsilon 4 allele frequency was 60% higher than it was in controls. Inheritance of epsilon 4 seems to confer risk of premature ischaemic heart disease in males, homozygotes being especially at risk at a younger age.