The alpha 1-antitrypsin deficient subject (protease inhibitor (PI) phenotype ZZ) has an increased susceptibility to liver disease. The condition is most commonly identified in early infancy as a conjugated hyperbilirubinaemia with hepatitis (11%) or a bleeding state due to vitamin K malabsorption (2%). 50% of cases have cirrhosis and 25% die in the first decade of life. A further 2% present with cirrhosis in later childhood. Adult males are at risk of hepatoma development with or without cirrhosis. Diagnosis is by isoelectric focussing or allele-specific oligonucleotide hybridization. The treatment is that of cholestasis and cirrhosis including transplantation. The pathobiology of the deficiency state, the mechanism of liver damage and the vulnerability of the newborn liver are discussed in this review. A plea is made for a trial of infusions of alpha 1-antitrypsin in early infancy, as is used safely but without proven efficacy in the emphysematous PIZZ subject. Prospects of therapy by gene modification are also reviewed.