Between July 1985 and June 1989, 19,432 newborns were screened during the first days of life to determine their Pi (protease inhibitor) phenotype. Fourteen infants were identified to be carriers of the PiSZ phenotype. Their clinical and biochemical follow-up data were recorded at 2, 5, and 12 months of age; only one case underwent a liver biopsy due to repeated abnormal liver enzymes. Three of 14 PiSZ infants showed some hepatic dysfunction at 2 and 5 months of age, but at 12 months all patients had normal liver function tests. None of them had clinical, biochemical, or morphological signs of neonatal cholestasis. The clinical and biochemical data related to the liver involvement are similar to those of the PiMZ phenotype, though the serum levels of alpha 1-antitrypsin in PiSZ carriers match those of the PiZZ group.