The liver is the principal organ for the synthesis of “transportable” proteins. The most important, quantitatively, is albumin. Functionally, however, the various blood-clotting pro-enzymes synthesized by the liver are of equal significance, since their much shorter half-lives lead to their earlier depletion in patients with liver disease with consequent risk of hemorrhage. Other enzymes transported from the liver to the plasma compartment include pseudocholinesterase, and lecithin cholesterol acyltransferase, as well as hepatic triacyglycerol lipase, releasable by heparin, and assuming increasing importance in the disposition of circulating lipoproteins. Chronic liver disease is associated with diminished levels of these proteins and enzymes in the plasma, and they generally correlate with each other and with the severity of hepatic insufficiency. More recent insight into the pathophysiology of hepatic protein biosynthesis has come from studies of collagen prolyl hydroxylase activity. This is increased in proportion to the amount of fibrous tissue in cirrhotic liver, and the increase precedes histological evidence of frank fibrosis. It may therefore prove to be a “marker” for those patients with alcoholic degeneration whose livers are committed to irrevocable progress towards cirrhosis. Derangement of hepatic glycoprotein biosynthesis may now be detected by measuring the serum concentration of desialylated glycoproteins which are increased in hepatic disease; the assay system utilizes an elegant variation of competitive protein binding. The phenomenon of hepatic microsomal enzyme induction has been known for almost two decades. Basic research is now generating clinical applications. For example, indices of hepatic microsomal enzyme induction have been used as adjuncts to therapeutic drug monitoring in assessing response to and compliance with drug therapy in many clinical situations. Drug clearance, a function of inducible hepatic microsomal enzymes, is now being explored as a test of hepatic function. Several recent studies indicate that clearance of antipyrine and similar compounds which may be measured chemically, or by the appearance of 14 CO 2 in the breath after administration of radio-labelled drugs, may prove valuable as diagnostic tests in hepatobiliary disease. It has been claimed that they are more sensitive than most established tests in detecting compromised liver function, although their ability to discriminate between various hepatobiliary diseases has not been established.