Eleven adult individuals (aged 24 to 66 years) with severe alpha1-antitrypsin deficiency, Pi Z, and with no clinical signs of liver disease, were investigated with a broad spectrum of liver function tests. Except for low alpha1-antitrypsin levels, no evidence of abnormal hepatic protein synthesis was found. Neither could any biochemical signs of liver cell necrosis or increased liver cell regeneration be disclosed. In spite of the well-known pronounced distension of hepatic endoplasmic reticulum (E.R.) by aggregated asialo-alpha1-antitrypsin in this disease, the function of the E.R. tested with the aminopyrine breath test was not found to be impaired.