The possibilities to screen atrophic corpus gastritis with serum pepsinogen I (S-PGI) and serum gastrin (S-gastrin) concentrations have been studied in 774 subjects: 71 index subjects selected from a general population at random, 353 of their first-degree relatives, 276 first-degree relatives of patients with gastric cancer, 53 patients with pernicious anaemia, and 21 of their relatives. Discrimination function analysis was calculated from members of random and gastric carcinoma families. S-PGI less than 30 ng/ml had a high sensitivity for severe diffuse atrophic corpus gastritis (SDAG) alone (89.5%) and SDAG + severe patchy atrophic corpus gastritis (SPAG) (89.1%). Respective figures for specificity were 91.5% and 94.8%. The discriminatory power of S-PGI less than 30 ng/ml and S-PGI less than 25 ng/ml was of the same order. The sensitivity of low S-PGI decreased sharply in detection of slighter forms of atrophic corpus gastritis. The sensitivity of S-gastrin greater than 100 pmol/l to discriminate SDAG was 57.9% and SDAG+SPAG 58.7%. Respective figures for specificity were 90.2% and 92.2%. Diffuse and patchy atrophic changes behaved similarly regarding S-PGI and S-gastrin mean concentrations. Accordingly, the biopsy specimen with the severest atrophic changes indicates the degree of atrophy, which associates closely with the changes in S-PGI and S-gastrin. In conclusion, severe atrophic (diffuse or patchy) corpus gastritis may be screened from a general population with high sensitivity and specificity by low S-PGI less than 30 ng/ml, whereas an increased level of S-gastrin is too insensitive for this.