We conducted a study to assess the effect of human immunodeficiency virus (HIV) infection on humoral immunity. Fifty-five homosexual men and 19 heterosexual men had four- to six-week postimmunization antibody responses measured to trivalent influenza vaccine and 23-valent pneumococcal vaccine. The homosexual men were divided into three groups: 20 asymptomatic HIV-seronegative men, 10 asymptomatic HIV-seropositive men, and 25 HIV-seropositive men with persistent generalized lymphadenopathy. Antibody responses to influenza antigens in the subgroups of homosexual men did not significantly differ from those of heterosexual controls. The IgG antibody responses to pneumococcal capsular types 9N and 18C in men with lymphadenopathy, and type 18C in HIV-seronegative homosexual men, were lower than those of heterosexual controls. Otherwise, responses to other ten capsular types showed no significant differences. There was no evidence of an immunosuppressive effect of vaccination on T-cell numbers, or deterioration of clinical status associated with vaccination. This study demonstrates that HIV-infected homosexual men, asymptomatic or with persistent generalized lymphadenopathy, are able to mount appropriate antibody responses to two commonly used vaccines.