The inheritable causes of jaundice comprise a large group of conditions of varying frequency, from Gilbert's syndrome which is relatively common, to the very rare Crigle-Najjar syndrome. Although these conditions have been well characterized clinically and in some cases biochemically, the underlying molecular defects were unknown because of a lack of knowledge about the process of bile secretion by hepatocytes. The recent cloning of several transporters for bile acids and other organic anions has enabled a greater understanding of this process and allowed correlation of the malfunction of these genes with specific disease processes. This new knowledge will provide for precision in diagnosis, allow antenatal testing and provide opportunities for gene therapy for some of the more serious disorders.