An investigation was carried out to determine whether amyloid could be detected in the dental periapical lesions or gingival buccal fold, or in both, of patients with rheumatoid disease but in whom amyloidosis had not been diagnosed. Tissue from the dental periapical lesions of 36 rheumatoid and 23 control patients, as well as from the gingival buccal fold of 11 of the rheumatoid and 11 of the control patients, were examined by the direct immunofluorescence technique and by polarization microscopy of sections stained with Congo red. Amyloid was observed almost 5 times more often, or in 19% of the dental periapical lesions of rheumatoid patients: it was detected by immunofluorescence in 7 rheumatoid patients and 1 control patient, and by polarization microscopy in 6 of these 7 rheumatoid patients as well as in the 1 control. Rectal biopsies performed on these 8 patients were positive in only 1 of the rheumatoid patients. Amyloid was not detected in any of the gingival biopsies. Serum samples from the rheumatoid and the control patients were tested for the presence of the nonimmunoglobulin amyloid fibril-related serum component, protein ASC. Nineteen of the 36 rheumatoid patients, including the 7 whose dental periapical lesions contained amyloid, had protein ASC in their serum.