The pathogenesis of lipoprotein-X in cholestasis is not totally resolved. Normally, the liver excretes lipoprotein complexes into the bile showing phospholipid and unesterified cholesterol concentrations similar to Lipoprotein-X. The in vitro incubation of these bile lipoproteins with serum or albumin leads to the appearance of Lp-X–like particles. These findings suggest that the reflux of bile into the plasma compartment causes the formation of lipoprotein-X in cholestasis as a result of a physicochemical, nonmetabolic process. On the other hand, lipoprotein-X particles found in familial LCAT deficiency are identical to those in cholestasis regarding ultrastructure and biochemical composition. It has been supposed that reduced LCAT activities, common in patients with hepatocellular disease, cause, alone or in combination with other factors, the formation of Lipoprotein-X in cholestasis. Lipoprotein-X is mainly removed by the reticuloendothelial system of the liver and the spleen, as shown by studies using radioactively labeled lipoprotein-X in rats. Other organs, such as the kidney, also actively clear Lipoprotein-X from the plasma.