Anti-pneumococcal IgM, IgG1, IgG2, and IgA antibody titers were determined in 61 pediatric patients with recurrent bacterial respiratory tract infections. The patients were divided in those with normal serum Ig levels (group 1, n = 46) and patients with dysimmunoglobulinemia (group II, n = 15). antibody titers to five pneumococcal serotypes (3, 4, 6A, 9N, and 19F) of different immunogenicity were determined by ELISA, before and 14 d after immunization with pneumococcal polysaccharide vaccine. In the patients of group I, IgM responses did not vary between the various serotypes. IgG1 antibodies reached high levels for pneumococcal types 3, 4, and 9N compared with an adult reference hyperimmune plasma pool, but remained low for the weak immunogenic types 6A and 19F. IgG2 antibody titers remained low and were nearly absent in 20/46 patients. The fold increase in IgA was high, but the ultimate IgA antibody levels remained low. IgA levels remained low to absent in 10/46 patients. Two patients (4%) of group I failed to show antipneumococcal antibodies of all Ig isotypes. In group II, 6/15 patients (40%) made no anti-pneumococcal antibodies of any isotype, whereas the remaining patients made no IgG2 and/or IgA anti-pneumococcal antibodies. We conclude that the frequency of nonresponders to pneumococcal vaccination in patients with normal serum Ig is low (4%). However, low IgG2 anti-pneumococcal levels are found in approximately 50% of the patients. In patients with dysimmunoglobulinemia, IgA and IgG2 responses were absent in virtually all patients, whereas 40% made no anti-pneumococcal antibodies of any isotype.