We analyzed blood samples from 407 healthy Swedish individuals, 244 men and 163 women, ages 17 to 86 years, for apolipoprotein (apo) E isoforms and serum triglycerides, low-density lipoprotein (LDL), high-density lipoprotein (HDL), and total cholesterol. Parallel genotyping by means of polymerase chain reaction (PCR)-amplified DNA was performed in 200 subjects. Identical results were obtained by genotyping and phenotyping in 95% of all subjects analyzed. The apo E allelic frequencies were 7.8% for epsilon 2, 71.9% for epsilon 3, and 20.3% for epsilon 4. Compared with other Caucasian populations, the present population had a high relative allelic frequency of epsilon 4. The epsilon 4 frequency decreased with increasing age and was significantly lower in individuals > 60 years of age (14.7%). When controlling for age and sex, there were strong correlations between total serum and LDL cholesterol and the various epsilon alleles. The epsilon 4 and epsilon 3 alleles correlated positively with serum cholesterol and the epsilon 4 allele correlated positively with LDL cholesterol. In contrast, HDL cholesterol and serum triglycerides did not show any correlation to the allele types. Thus, the results demonstrate a considerable age variation of the epsilon allele frequency among healthy Swedes and an influence of apo E alleles on serum and LDL cholesterol concentrations.