The sensitivities, specificities, and predictive values of parietal cell antibody, serum gastrin, and serum pepsinogen I (PG I) for severe atrophic gastritis of the oxyntic gland mucosa have been determined in 171 first-degree relatives of 62 patients with pernicious anemia. Parietal cell antibody had the lowest sensitivity (65%), specificity (87%), and predictive value (44%). A low serum PG I and a high serum gastrin had identical specificities (97%), and similar predictive values (84 vs 83%), but the sensitivity of a low serum PG I was greater than that of a high serum gastrin (91 vs 83%). Parietal cell antibody was found in 19 of 148 relatives without severe atrophic gastritis and occurred as an isolated finding in 17. In contrast, 14 of the 15 relatives with severe atrophic gastritis who had parietal cell antibody also had a high serum gastrin and a low serum PG I. A high serum gastrin together with a low serum PG I had a specificity of 100%. The results recommend serum PG I and serum gastrin, but not parietal cell antibody, as tests for severe atrophic gastritis in relatives of patients with pernicious anemia.