The liver performs a wide range of physiologically important functions, including the synthesis and secretion of albumin, fibrinogen, and other plasma proteins; the synthesis of cholesterol and bile acids, and the metabolism of drugs, steroids, and amino acids. The liver has a central role in energy metabolism as the major store of glycogen, as the site of gluconeogenesis, and in the synthesis of fatty acids and triglycerides. The liver is, therefore, a vital organ, but it is difficult to study specific liver functions in vivo owing to interfering influences from other organs, e g., the kidney, gut, and lungs, which metabolize drugs and the muscle involvement in glucose homeostasis. An isolated liver preparation seems necessary, and the isolated human hepatocyte appears to be a suitable experimental model for the study of liver-specific functions.