The interaction of steroid hormones with individual classes of lipoproteins and apoproteins was analysed. Plasma lipoproteins bind steroid hormones and can therefore play a role in their active transport in the body. High density lipoproteins demonstrate the highest affinity for steroids. The lipoprotein-steroid complex formation involves the protein components of lipoproteins with the apolipoprotein A-I as one of the protein components responsible for the binding of steroid hormones. The constants of the complex formation between lipoproteins and steroid hormones suggest specificity of this binding. The reviewed data suggest a real possibility of penetration of steroid hormones into cells by a receptor-mediated endocytosis using the apolipo-protein complexes as a vehicle. ApoA-I immuno-reactivity in the liver nuclei is due to two proteins. One 28-kD protein corresponds to the mature form of the plasma pool of apoA-I and another 14-kD protein is product of limited proteolysis of apoA-I. The highest content of apoA-I immuno-reactivity was detected in transcriptionally active chromatin and nuclear matrix. ApoB immuno-reactivity is due to six proteins with molecular weights from 15 to 100 kD. ApoE immuno-reactivity is due to a single protein corresponding to the 35-kD form of plasma apoE. ApoA-I, apoB and apoE may be involved in the regulation of transcriptional activity of chromatin. A novel mechanism of protein biosynthesis regulation in liver under the action of reduced forms of steroid hormones (tetrahydrocompounds) and apolipoprotein A-I is discussed.