The molecular genetics of five common single gene and one polygenic chronic liver disease is discussed. In two of the single gene disorders, alpha 1-antitrypsin deficiency and cystic fibrosis, the gene responsible is now known and the repertoire of different mutations underlying the disease is being defined. In the other three single gene defects (haemochromatosis, polycystic liver disease and Wilson's disease) the chromosomal location of the disease allele is known. It is anticipated that recombinant DNA techniques will enable the genes responsible for these diseases to be cloned in the near future, thus allowing the biochemical abnormalities to be defined through reverse genetics. In many chronic liver diseases the relative contribution of genetic and environmental factors remains unclear. Evidence suggests there is a definite genetic component in predisposition to alcoholic cirrhosis; the role of putative candidate genes is discussed. It is hoped that the definition of a genetic locus linked to alcoholic cirrhosis will ultimately teach us more about the basic pathogenesis of this disease.