We tested apolipoprotein E phenotypes in 1557 normolipidemic factory workers and 822 hyperlipidemic hospital patients. We distinguished six different apolipoprotein E phenotypes and determined their frequencies in normolipidemia (factory workers), hypertriglyceridemia, hypercholesterolemia, and mixed hyperlipidemia. For the three homozygous phenotypes E3/3, E4/4, and E2/2, the percentage distribution in the normolipidemic group was 62.2%, 2.2%, and 0.9%, respectively; for the three heterozygous phenotypes E4/3, E3/2, and E4/2, we determined frequencies of 19.9%, 11.7%, and 2.9%, respectively. A higher prevalence of E2/2 homozygosity was observed in hypertriglyceridemic persons (2.5%) and persons affected by mixed hyperlipidemia (5.0%). E4/4 homozygosity occurred more often among hypercholesterolemic patients (5.0%) than normolipidemic persons (2.2%). These data suggest that E2/2 homozygosity and E4/4 homozygosity both predispose to hyperlipidemia. Patients affected by mixed hyperlipidemia should be investigated for their apolipoprotein E polymorphism because of the possible linkage of apolipoprotein E2/2 homozygosity, hyperlipidemia, and atherosclerosis.