Antibody responses to pneumococcal vaccine were studied in asymptomatic heterosexual partners of persons with AIDS and intravenous drug users seropositive for human immunodeficiency virus (HIV). Serum antibodies to 12 pneumococcal capsular antigens were measured by radioimmunoassay. Eleven intravenous drug users seropositive for HIV, 13 seronegative intravenous drug users, and 10 each seropositive and seronegative sexual partners received 23-valent pneumococcal vaccine. Additional unvaccinated matched seropositives served as controls. Antibody responses were significantly lower among subjects seropositive for HIV (P less than .05). Fourteen (88%) of 16 seropositive subjects with baseline type-specific antibodies to one or more pneumococcal antigens less than 300 ng of antibody nitrogen/ml (ngAbN/ml) demonstrated a rise in one or more of these antibodies to greater than 400 ngAbN/ml. No clinical deterioration or decrease in T4 cells attributable to vaccination was found. Although antibody responses to pneumococcal vaccine among HIV-infected subjects were impaired, most with antibody levels less than 300 ngAbN/ml developed titers of one or more type-specific antibodies to levels greater than 400 ngAbN/ml without notable adverse effects.