The objective of this study was to examine vaccine type-specific antibody titers eight months after a five-valent pneumococcal conjugate vaccine (PCV) in human immunodeficiency virus (HIV) and non-HIV-infected children under two years of age. Sixteen HIV-infected and 14 non-HIV-infected children under two years of age, and of similar age, race and sex distribution, received three doses (separated by two months each) of a five-valent oligosaccharide PCV (types 6B, 14, 18C, 19F, and 23F separately coupled to diphtheria CRM197). An additional 11 non-HIV-infected children, of similar demographic distribution to the PCV groups, received three doses of saline placebo. sera were collected just prior to, and at one and eight months after the three study drug doses. Serum vaccine type-specific pneumococcal IgG antibodies were measured by enzyme-linked immunoabsorbant assay (ELISA). There was an impressive rise in antibody titers pre- to one month post-third PCV in both the HIV (58-970-fold) and non-HIV-infected (19-553-fold) children. There was a rapid and similar drop in antibody titers eight months after the PCV series for both HIV (range 69-87% drop) and non-HIV-infected (range 57-79% drop) subjects respectively. However, 46% of the antibody titers from HIV-infected children and 62% of the titers from non-HIV-infected children were still > 1.0 microgram ml-1 compared to placebo recipients for whom only 5% of the titers were > 1.0 microgram ml-1 (p < 0.05). At the eight month post-PCV series blood draw, there were no significant differences in the GMTs, the percent drop in titers, or proportion of titers > 1.0 microgram ml-1 between the five HIV-infected children who had advanced (CDC class: N3, A3, B2-3, C1-3) compared to the 11 children with mild (CDC class: N1-2, A1-2, B1) HIV disease at the time of their first PCV dose. Eight months after the PCV series, the proportion of titers (combined all five serotypes) > 1.0 microgram ml-1 was slightly, but significantly, lower for HIV-infected subjects (46%) compared to non-HIV-infected subjects (62%) (p < 0.05). These data are helpful in describing the kinetics of antibody responses to pneumococcal conjugate vaccines in both HIV and non-HIV-infected young children.