The specific antibody response of the adenoids to a respiratory antigen was investigated, both in vitro and in vivo. The in vitro immunoglobulin (Ig) production of adenoidal and tonsillar lymphocytes in the same patient in 18 cases was measured by an enzyme-linked immunosorbent assay. Adenoidal lymphocytes produced more IgM than IgG or IgA under culture conditions without any mitogens, whereas IgG was the major Ig produced by tonsillar lymphocytes. The same results were obtained when cultured with pokeweed mitogen. Under culture conditions with Dermatophagoides farinae (mite) antigen, adenoidal lymphocytes produced only specific IgM class antibody, and at a level significantly greater than tonsillar lymphocytes. Through an in vivo study, we established experimental adenoidal tissue in the guinea pig by long-term exposure to an ovalbumin aerosol. Infiltration of cells producing the specific antibody against an ovalbumin was demonstrated in the epipharyngeal mucosa using immunofluorescent staining. Our results confirm that the adenoids play a role in specific immune responses to respiratory antigens.