We have compared acidity level and Helicobacter Pylori contamination rate of the mucous coat of stomach in 50 patients with duodenal ulcer at the age from 17 to 54 y.o., among which were 25 smokers and 25 non-smokers. The period of smoking varied from 5 to 21 years. In the morning Ph-measurements were carried out by means of IAS-2 device based on V. N. Chernobrov's method. We used fibrogastroduodenoscopy technique for verifying a duodenal ulcer and obtaining mucous coat material from antrum and corpus ventriculi to obtain Helicobacter Pylori contamination rate. The acid level of the stomach in the smokers was shown to be reliably lower than in non-smoking patients, what was the cause of higher Helicobacter Pylori contamination rate.