The labial salivary glands of 81 patients with rheumatoid arthritis (RA) and those of 45 control (CO) patients were biopsied. Mast cell counts were compared with the number of other inflammatory cells (B- and T-lymphocytes and mononuclear phagocytes, stained with acid-alpha-naphthyl acetate esterase technique (ANAE) and to fatty change and fibrosis. Mast cells were directly related to the amount of fibrosis and fatty change in both series, supporting the recent theory that these changes are age-related phenomena and not caused by RA per se. Mast cell counts increased slightly with increasing inflammatory cell infiltration, but no correlation could be found between mast cell counts and B or T cells. Mononuclear phagocyte system (MPS) cells were fewer in the RA group than in CO patients, possibly suggesting an impaired phagocytizing capacity in their salivary glands. In many respects the results are consistent with the known functions of tissue mast cells. Their role in the labial salivary glands is discussed in the light of current immunopathologic concepts of RA and lesions associated with it, i.e. Sjögren's syndrome.