To evaluate the validity of serum pepsinogen levels as a screening tool for gastric cancer and adenoma, immunoradiometric assays of serum pepsinogen I level (PG I), II level (PG II) and esphagogastroduodenal endoscopies were done in 757 health examlnees. Serum PG I level was higher in subjects with active duodenal ulcer (n=45, 75.2+/-34.3 microgram/l(mean+/-standard deviation), p<0.01) and gastroduodenal ulcers (n=8,756+/-19.8 microgram/l, p<0.05), and was lower in those with gastric adenoma (n=4,37.7+/-37.2 microgram/l, p<0.2) than those with normal, mild gastritis findings or ulcer scars (n=378, 56.6+/-24.9 microgram/l). Serum PG II level las higher in subjects with active duodenal ulcer (17.2+/-13.8 microgram/l, p<0.2), active gastro-duodenal ulcers (l8.3+/-7.4 microgram/l, p<0.2) and gastric carcinoma (n=3, 23.8+/-10.9 microgram/l, p<0.05) than those with normal, mild gastritis findings or ulcer scars (14.5+/-7.9 microgram/l). Serum PG I/PG 11 ratio was higher in subjects with active duodenal ulcer (5.1+/-1.6, p<0.05) and was lower in those with chronic gastritis (n=107, 4.1+/-1.7, p<0.05), gastric polyp (n=19, 3.9+/-1.4, p<0.2), gastric adenoma (n=4, 2.1+/-1.9, p<0.01) and gastric carcinoma (n=3, 2.7+/-1.2, p<0.1) than those with normal, mild gastritis findings or ulcer scars (4.5+/-1.7). Serum PG 11 level increased with age until 6th decade, whereas serum PG I/PG II ratio decreased with age in 378 subjects with normal, mild gastritis findings or ulcer scars. The screening criteria of serum PG I<70 microgram/l and PG I/PG II ratio<3.0 for detecting gastric cancer and adenorna gave a positive rate of 15.7%, sensitivity of 57.1% and specificity of 84.7%.