Several studies have indicated that genetic polymorphism of apolipoprotein (apo) E is related to coronary artery disease (CAD). We therefore determined the apo E phenotype in 91 consecutive Finnish men with angiographically confirmed CAD. The apo E phenotype distribution differed significantly from that observed in the Finnish population (p less than 0.05). In the patient group, the frequency of the epsilon 4 allele was 0.324, which is 1.4-fold higher than in the normal Finnish population and twice as high as in other Caucasian populations. Serum lipoproteins and postheparin plasma lipase activities did not display any significant variation according to apo E phenotype. These studies confirm and extend, in a population with high epsilon 4 allele frequency, the previous data on the impact of the epsilon 4 allele on the risk of CAD and suggest that the high epsilon 4 allele frequency in the Finnish population may be one factor contributing to Finns' increased susceptibility to CAD.