AbstractThe widespread use of anovulatory compounds and the well‐known effects of sex hormones on various aspects of metabolism prompted this review of our work and the work of others on observed changes in lipid metabolism resulting from the administration of oral contraceptives and their components. In the rat, female sex hormone administration results in a decreased plasma cholesterol level, an accumulation of cholesterol in liver and a decreased hepatic cholesterol biosynthesis. On the other hand, cholesterol biosynthesis is enhanced in ovaries and adrenals. There is also a diminished alpha lipoprotein content and a corresponding decrease in the alpha/beta lipoprotein ratio. In some cases these changes are comparable to those observed during pregnancy. The results of sex hormone administration to women are more variable. In this case the most often observed effect is hypertriglyceridemia. Changes in lipoprotein content and distribution are also evident and may be the result of changes in metabolism in the liver, e.g., lipid synthesis or lipid transport from liver to plasma and tissues, or both. Many of these changes may be mediated indirectly through the action of estrogenprogestin on other hormones. In both species the effects of oral contraceptives are attributable principally to the estrogen component. The combination of estrogen with progestin compounds, which constitutes the oral contraceptive, modifies the effects of estrogen administered alone.