We immunize a large group of preschool asthmatics (2-5 years old) sequentially: one dose of seven-valent pneumococcal conjugate vaccine (PCV-7) followed by a single dose of 23-valent pneumococcal polysaccharide vaccine (PPV-23). We randomly assign half of the vaccinees to receive PPV-23 eight weeks after PCV-7 (group A), and the rest to a 10-month interval (group B). Pneumococcal antibody concentrations to serotype 4, 5, 6B, 7, 9V, 14, 18c, 19F, and 23F are determined initially, after two, and 12 months after PCV-7. Local and systemic reactions to each vaccine are recorded.