Detection of autoantibodies, HLA typing and immunofluorescence studies on gastric biopsies were carried out in subjects with histologically proven chronic atrophic gastritis (CAG) and chronic superficial gastritis (CG). All were seronegative for parietal cell antibody and did not have pernicious anemia. Except for positive antismooth muscle and antimitochrondrial antibodies in one patient with CAG, autoantibodies (antinuclear, smooth muscle, mitochrondrial, parietal cell) were absent in patients with CAG and CG. Immunofluorescence studies showed that Ig-G and IgA were presented in the lamina propria of all cases with CAG or CG and of subjects with normal gastric histology. Ig-M was seen less often, in about half the cases. Complement C3 was an uncommon finding, being positive in only one case with CAG and one case with CG and in none of the cases with normal gastric histology. Fibrinogen was more commonly seen in patients with CG (5/5 cases) than in those with CAG (3/11 cases). Fibrinogen was found in one case with normal gastric histology. The most consistent fluorescence was obtained with antiparietal cell antiserum. All subjects with CAG showed negative or weak staining only. In contrast, subjects with CG and normal gastric histology had strong specific fluorescence. An increased frequency of HLA-A1 plus HLA-B8 was found in subjects with CAG (20.7% in controls; 40% in CAG).