Sex steroids are important regulators of apolipoprotein synthesis and metabolism in a wide variety of species. In man, epidemiological studies have established strong correlations between sex steroid levels, circulating apolipoprotein profiles, and atherosclerotic risk. In this review, we compare data obtained from studies on two model systems that are being used to examine molecular mechanisms by which estrogens and androgens may influence hepatic lipoprotein synthesis. The first involves estrogen-dependent induction of lipoprotein synthesis in avian liver and the second involves estrogen-dependent modulation of lipoprotein synthesis in the human hepatocarcinoma cell line HepG2.