The last decade has seen tremendous developments in many fields of gastroenterology and hepatology. The aim of this series is to highlight some of these topics that deserve particular interest. Research in the field of viral hepatitis has been very intense and successful in recent years. The hepatitis B virus is one of the best explored at the current level of virology. Not only the nucleotid sequence of the viral DNA can be decoded, but also the amino acid compounds of its genetic products are known today. Since the techniques of molecular biology have increasingly found access to clinical laboratory use, hepatitis B virus infection can serve as an example for the importance of molecular biology in clinical hepa- tology. Another example for the interdependence of basic science and clini- cal medicine represents the research on bile acid metabolism. The investigation of bile acids has revealed new diagnostic approaches to hepatic and intestinal disorders. Commercial kits for the routine measurement of serum bile acids in clinical laboratories by enzymatic or radioimmunologic techniques are now available. The diagnostic value of these measurements in gastroenterology and hepatology shall be defined. Another aspect of bile acid research leads to new per- spectives in the treatment of gallstone disease. The dissolution of cholesterol gallstones by chenodeoxycholic acid (therapy) may be quoted as the best example for the development of new phar- macotherapeutic principles derived from basic bile acid research.