Apolipoprotein (apo) E phenotype was examined in 188 healthy subjects and in 447 patients seen between 1984 and 1986. The frequency of the apo E2, 3, and 4 genes in the clinically healthy subjects was 0.035 +/- 0.0288, 0.872 +/- 0.0310, and 0.093 +/- 0.0152, respectively. The frequency of the apo E3 gene was higher and that of the apo E genes 2 and 4 lower than that reported in western countries. Clinical features and apo E phenotype are presented from the 5 patients with type III hyperlipoproteinemia (HLP) due to apo E phenotype E2/2 (E2-III); all patients in E2-III were post-menopausal women. In contrast to the clinical characteristics so far reported, no notable findings of atherosclerosis, such as coronary angiographic findings or xanthoma, were evident in any of these 5 patients. Glucose intolerance was seen in 4 of them. Four patients were normolipidemic with apo E phenotype E2/2 (E2-N). In addition, plasma lipid and apolipoprotein concentrations were determined in patients with different apo E phenotypes. Plasma total cholesterol (TC) and apo B levels were elevated in the order of E2-N, E2/3, E2/4, E3/3, E3/4 and E4/4 except for E2-III. The plasma apo E level was highest in E2-III but was not significantly different from other phenotypes. The apo B/apo E and apo C-III/apo E ratios were significantly lower in E2/2 than in other phenotypes. The TC/apo B ratio was significantly higher in E2/2 than in other phenotypes.