Until 15 to 20 years ago, immunologists believed that the ability of the young human infant to produce antibodies was extremely poor. Even though this ability gradually increased with age, it was not considered to reach a significant capacity until after several months of life. Investigations during the past 2 decades, however, have thrown new light on the subject and have shown that the young infant is able to produce antibodies more effectively than previously suspected. The purpose of this paper is to review the general problem of antibody formation in infancy by examining some of the experimental and clinical data obtained in recent years. Characterization of Antibody Electrophoretic methods, using the principle that proteins in solution migrate at different rates at a given pH under the influence of an electric current, have permitted the characterization of serum in terms of different protein components. Thus, by paper electrophoresis, the serum