The purpose of this study is to elucidate the relationship between apolipoprotein (apo) E polymorphism and plasma lipid profiles and the frequency of hyperlipoproteinemia (HLP) in obesity. Eighty-seven obese subjects with 131 percent of ideal body weight (mean) were studied. One hundred and thirty-two nonobese subjects with 105 percent of ideal body weight were also selected as the controls. There was no significant difference in apo E allele and phenotype frequencies between the obese and nonobese subjects. The frequency of HLP was 100 percent in obese subjects with apo E2 and/or apo E4, whereas it was 47.3 percent in obese subjects with the common apo E3/3 phenotype. In obesity apo E2 was associated with increased plasma triglyceride (TG) and apo E, and decreased plasma high density lipoprotein (HDL) cholesterol (type III and IV HLP), whereas apo E4 was associated with increased plasma TG, total cholesterol, and apo E (type IIa, IIb, IV and V HLP). These results indicate that obese subjects with apo E2 and/or E4 were more susceptible to HLP than obese subjects with the common apo E3/3 phenotype. It is concluded that apo E2 and/or E4 are closely related to HLP in obesity and thus may be one factor linking obesity with cardiovascular disease.