Available pneumococcal vaccines provide only limited protection for certain at-risk populations. Fifteen healthy young adults and 11 older chronic bronchitics received 23-valent pneumococcal vaccine. ELISA showed that IgG reactive with capsular polysaccharides from Streptococcus pneumoniae serotypes 3, 4, 8, 14, and 19F increased after vaccination. Bronchitics exhibited lesser responses for four of these serotypes, although differences between the groups were significant only for serotype 3. Adsorption of postvaccination sera with pneumococcal cell wall polysaccharide significantly reduced mean antibody levels in both groups and lowered the proportion of sera that demonstrated type-specific antibody responses. Reactive IgG was largely restricted to the IgG2 subclass. Pneumococcal vaccine may provide suboptimal protection of older adults because antibody responses to some capsular polysaccharides are lower in elderly bronchitics than in healthy young adults. A substantial proportion of measured antibody reflects IgG reactive with cell wall polysaccharides rather than with type-specific, capsular constituents, suggesting that antibody responses in subjects of all ages deserve reappraisal.