Two hundred thousand infants born in Sweden between November 1972 and September 1974 were screened at birth for alpha 1-antitrypsin (alpha 1 AT) deficiency. At age 4 years 172 of 183 children with alpha 1 AT deficiency were examined and compared with 80 randomly selected control children. The children with alpha 1 AT deficiency had the following Pi types: 118 PiZ, 50 PiSZ, 2 PiZ-, 1 PiS-, 1 PiFZ. Two PiZ children have severe liver cirrhosis and 1 PiZ boy had died of aplastic anemia. Abnormal levels of serum alanine aminotransferase (S-ALAT) were found in one PiSZ and 47 PiZ children. Upper and lower respiratory infections, otitis, eczema, urinary infections or complications of child diseases did not occur more often in children with alpha 1 AT deficiency than in controls. More parents of alpha 1 AT deficient children had stopped smoking and their fathers smoked significantly less. Forty parents of children with alpha AT deficiency PiZ answered a questionnaire concerning their reaction to, knowledge about and attitudes towards neonatal screening for alpha 1 AT deficiency. Many parents reported having reacted with lack of understanding, shock or depression upon learning that the child had alpha 1 AT deficiency. About 4 years later 44% reported still lack of understanding, and 18% depression or feelings of guilt. About two-thirds had not fully understood why alpha 1 AT deficiency had been identified, despite the fact that they had seen their doctor 3--4 times for check-ups and counselling since birth.