Antibody deficiency syndromes are an important cause of recurrent infections in children. Today it is possible to perform a complete evaluation of antibody-mediated immunity leading to a definitive diagnosis of either normal or abnormal immunity in most patients. However, the interpretation of the results of IgG subclass determinations and specific antibody responses is still being defined. At this time our recommendation is that patients who meet the criteria for an evaluation of antibody-mediated immunity be referred to subspecialists trained in this evaluation until better criteria for normal have been developed. The possibility that protective amounts of antibodies against pneumococcal serotypes may develop only transiently must be considered in patients with recurrent infections after initial improvement after immunization, especially if IgG2 subclass deficiency is also present. In the future it may be possible to use a faster and more economical approach to evaluate patients with recurrent infections by immunization with pneumococcal vaccine and then measuring IgM, IgG and IgA along with postimmunization specific antipneumococcal antibody titers 4 to 6 weeks later. For this approach to become feasible, further studies comparing the information obtained from the evaluation of pre- and postimmunization antibody concentrations with that obtained from the evaluation of postimmunization concentrations alone are needed.