Immunofluorescence studies of plasma cells were performed on small intestinal and colonic biopsies obtained from a series of patients with acquired immunodeficiency syndrome or the "AIDS related complex" plus homosexual male and heterosexual controls. The AIDS group was significantly depleted of IgA plasma cells compared to the control groups. In contrast, the numbers of IgM plasma cells were increased in the AIDS and homosexual control groups compared to the heterosexuals. Plasma cell fluorescence intensities for IgA and IgM were decreased in the AIDS patients, implying less cytoplasmic immunoglobulin per cell. The frequency of IgA plasma cell depletion did not differ in men and women, patients with opportunistic infections or Kaposi's sarcoma, or in patients with and without gastrointestinal symptoms. The extent of IgA plasma cell depletion did not correlate with serum IgA concentrations. IgA plasma cell numbers also did not correlate with selected parameters of nutritional status and intestinal absorption. Studies of salivary IgA output demonstrated decreased secretion of soluble IgA in AIDS patients, and an increased secretion of IgA in particulate form. These results suggest that abnormalities in IgA secretion occur in AIDS and might influence its clinical manifestations.