IgA-, IgM- and IgG-containing immune complexes (CIC) were detected in 48, 19 and 12% of 52 patients with primary Sjögren's syndrome (SS), in 36, 38 and 56% of 45 patients with rheumatoid arthritis, and in 8, 5 and 3% of 40 normal controls. A high proportion of primary SS patients also had considerable amounts of serum IgA and elevated levels of IgA with rheumatoid factor (RF) activity. IgA-CIC and IgA-RF were more frequent (P less than 0.03 and less than 0.001) in the 27 primary SS patients with, than in the 25 without extraglandular manifestations. IgA-CIC could play a role in mediating the tissue injury associated with primary SS.