Nitrosamines are powerful carcinogens in animal .and they can be formed easily from nitrite by combining these with secondary, tertiary and quaternary amines. This reaction is influenced by nitrite concentration and pH of gastric juice, bacterial colonization and some inorganic ions in gastrointestinal tract. But there are few reports for nitrite concentration in gastric juice still yet. It should be more interesting to detect the nitrosamine concentration in gastric juice to find out the relationship to the stomach cancer, but the procedure itself is very complex. So we chose to examine the nitrite concentration and pH of gastric juice, and by comparing these two, we tried to detect the relationship of these to the various gastric and duodenal disorders. We selected 90 subjects and divided them into 5 groups normal, chronic gastritis, stomach ulcer, duodenal ulcer and stomach cancer according to the gastrofiberscopic findings and pathologic examination of biopsy specimen. The fasting nitrite concentration of gastric juice was measured and was compared to the pH of gastric juice. In this study, the mean gastric juice pH was highest in the cases of stomach cancer (1.85+-1.07 in normal subjects, 2.30+-1.28 in chronicgastritis, 2.78+-1.93 in stomach ulcer, 1.94+-1.25 in duodenal ulcer and 3.89+-1.71 in stomach cancer) and was statistically significant in normal subjects only. The nitrite concentration of gastric juice was highest in cases of stomach cancer(2.29+-0.53ug/ml) and was lower in order of stomach ulcer (l. 62+-1.32), duodenal ulcer (l.48+-1.18), chronic gastritis.(l.22+-1.70) and the normal subjects(0.95+-0.27), and the results in cases of stomach cancer, stomach ulcer and chronic gastritis were stastically significant. The gastric pH was significantly related to the nitrite concentration in the cases of stomach cancer, stomach ulcer and chronic gastritis. Also, the pH of overall subjects was significantly correlated to the nitrite concentration of gastric juice. But we couldn't find any correlation between the nitrite concentration and the age or sex of the subjects.