Measurement of pneumococcal antibody concentration is a frequently used parameter for functional antibody response to vaccination. Antibody concentration in response to vaccination and strength of antigen-antibody (avidity) interaction are both important measurements of functional antibody response. Both antibody concentration and avidity contribute to immunity against invasive pneumococcal disease. Higher avidity is correlated with increasing bactericidal activity and opsonophagocytosis. On the other hand, patients with lower pneumococcal avidity may be more likely to develop clinically significant pneumococcal sinopulmonary infections. Nine patients with recurrent bacterial respiratory infections were identified by retrospective chart review as having adequate pneumococcal antibody concentrations, but with low avidity for multiple serotypes following immunization with pneumococcal vaccine polyvalent (PPSV23). We assessed response with IgG replacement therapy in these patients. The mean number of serotypes with a normal antibody response (>1.3 mg/ml) among 9 children following immunization with pneumococcal vaccine polyvalent was 19.1 (range 12-22) of 23 serotypes while the mean number of serotypes with a normal avidity response (≥1.0) was 4.7 (range 2-7) of 23 serotypes. Flow cytometry was performed for 8 of the 9 patients prior to starting SCIG replacement therapy. 100% of the cohort experienced a significant decrease in yearly infection rate after starting immunoglobulin replacement. This is the first study to assess the clinical response to immune globulin replacement in patients with normal pneumococcal antibody response but poor pneumococcal avidity, and suggests that patients with poor pneumococcal avidity but apparent normal response by pneumococcal antibody following PPSV23 may benefit from IgG replacement therapy.