Apolipoprotein A-IV (APO A-IV) is a major protein component of mesenteric lymph chylomicrons and very-low-density lipoproteins. It is found in plasma predominantly unassociated with major lipoprotein fractions and in high density lipoproteins. APO A-IV exhibits structural heterogeneity owing to two codominant alleles, APO A-IV*1 and APO A-IV*2, that occur in Caucasian and black populations. In vitro experimental evidence indicates that APO A-IV may be a cofactor for the lecithin:cholesterol acyltransferase enzyme, may be involved in reverse cholesterol transport, and may play an important role in the modulation of lipoprotein lipase activity. In this study we have investigated the effect of two APO A-IV phenotypes, APO A-IV 1-1 and APO A-IV 2-1, on quantitative lipid measures in a group of 453 white women being followed through menopause for changes in cardiovascular risk. At baseline all women were premenopausal. Of the nine lipid measures, triglycerides showed a marginally significant effect caused by phenotype. The APO A-IV 2-1 heterozygotes had lower average triglycerides than the 1-1 homozygotes (P = .053).