The distribution of apolipoprotein (apo) E phenotypes was investigated in Japanese schoolchildren and an attempt was made to determine whether the apoE phenotypes influence the serum levels of lipid and lipoprotein. The subjects were 289 children from a junior high school (145 M, 144 F, aged 12-13 y). The E3/3 phenotype was demonstrated in 69.9%, E4/3 in 18.7%, E2/3 in 9.0%, E4/2 in 1.4%, E4/4 in 0.7% and E5/4 in 0.3%. E2/2 was not detected. Serum levels of total cholesterol and low-density lipoprotein-cholesterol were progressively lower in the phenotypes E4/3, E3/3 and E2/3. The serum level of high-density lipoprotein-cholesterol showed a progressive increase in the same order. In conclusion, Japanese schoolchildren with E4/3 already had an atherogenic serum lipid profile.