It is not known how long vaccine-induced type-specific pneumococcal antibodies persist or whether age-related changes in their avidity occur; we therefore administered pneumococcal vaccine to 15 elderly persons aged 60-67 years to determine the level and avidity of the pneumococcal antibodies before vaccination and again 4 weeks and 5 years later. Antibody levels were significantly higher after vaccination than before vaccination in 67% of these subjects (P < .01). On the basis of guidelines established for revaccination, we found that 60% of these elderly persons required revaccination 5 years after primary immunization and that the antibody status of the remaining 40% would need to be determined some years later. No significant differences in IgG antibody avidity were detected in connection with the type of pneumococcus, the vaccination status of the vaccinee (i.e., whether sera were assayed before vaccination or 4 weeks or 5 years later), or the age of the vaccinee.