A deficiency of the major serum α1-globulin, the α1-antitrypsin, was first described in five patients by Laurell and Eriksson in Sweden in 1963. It soon became obvious that severe α1-antitrypsin deficiency was familial, and highly associated with chronic lung disease, having its onset in the third or fourth decade of life. Since the early descriptions of this common deficiency state, it has become clearly associated with familial emphysema in some families, familial infantile cirrhosis in others, and occasionally with a combination of childhood lung and liver disease in siblings. For the pediatrician, severe α1-antitrypsin deficiency now enters into the differential diagnosis of both chronic pulmonary disease in childhood and obstructive jaundice in the newborn period. In addition, low levels of α1-anrirtysin in serum are characteristic of respiratory distress syndrome, and elevations of this protein may be found in a variety of clinical situations. The α1-antitrypsin probably functions as a major control protein against the tissue-damaging effects of both endogenous and exogenous enzymes. This review will cover several basic and clinical features of this protein with respect to its importance in pediatrics. CHEMISTRY AND METABOLISM A 50,000 molecular weight glycoprotein, the α1-antitrypsin is synthesized in the parenchymal cells of the liver and is secreted into serum as the major α1-globulin, comprising approximately 4% of the total serum protein level (normal concentrations are approximately 2.2 mg/ml). Alpha1-antitrypsin is present in many body fluids, having been found in microgram per milliliter quantities in nasal secretions, tears, saliva, pulmonary secrelions, duodenal fluid, cerebrospinal fluid, cobstrum, and mother's milk.