Persistence of antibodies to 23-valent pneumococcal vaccine was assessed among 62 subjects aged 65-88 years. IgG antibodies were measured by standardized EIA to serotypes 4, 6B, 9V, 14, 19F, and 23F before and 1 month, 1 year, and 3 years after vaccination. After satisfactory antibody responses (fold increases from 2.6 to 5.3), 3-year geometric mean concentrations (GMCs) had waned to close (for types 4, 9V, and 23F) or similar (for types 6B and 19F) to their prevaccination values. Type 14 was exceptional: 1-month GMC was 7.7-fold and 3-year GMC was 3.0-fold in comparison to the prevaccination GMC. Antibody concentrations decreased at an equal rate irrespective of serotype and age or sex of the vaccinee. The major factor predicting the persistence of antibodies above the prevaccination level was the magnitude of the original antibody response. Present results suggest that pneumococcal revaccination of the elderly may be needed as early as 3-4 years after the initial vaccination.