The paper presents the results of observations concerning the effect of cigarette smoking on the prevalence of peptic ulcer among 6,512 rural inhabitants aged 20-64, selected by two-stage sampling. Of these, 2,506 (38.6%) were regular smokers. In order to determine precisely the negative effect of smoking on the human body the nicotinic index was used (N.I.), calculated by multiplying the number of cigarettes smoked daily by the period of smoking (years). The three-stage scale of the nicotinic index was applied: I° - N.I.<100, II° - N.I. = 100-300, III° - N.I.>300. The mean value of the nicotinic index calculated for the total number of smokers in the study was 290.3. A statistically significant higher N.I. was observed in patients with peptic ulcer - 432.5, compared to patients with other diseases - 337.2, and healthy individuals - 203.3. Among patients with peptic ulcer the highest percentage of people with N.I. >300 was noted (59.0%), compared to patients with other diseases (42.9%) and those who were healthy (22.6%). The differences observed between patients with peptic ulcer and those of the remaining groups were highly statistically significant (p<0.001). The percentage of people with the lowest value of the nicotinic index (N.I. <100) in individual groups was: in patients with peptic ulcer - 13.5% (the lowest), among patients with other diseases - 25.0%, in the group of healthy individuals - 38.5% (the highest). An increase was noted in the incidence of peptic ulcer with the value of the nicotinic index. Peptic ulcer occurred in 3.8% of patients with N.I. < 100, in 6.4% of those with N.I. = 100-300, and in 13.2% of patients with N.I. > 300. An increase in the percentage of patients with the nicotinic index was observed irrespective of the site of ulcer. It became most evident among patients who underwent surgical treatment due to peptic ulcer, where the highest value of the nicotinic index (N.I. > 300) was noted in 79.5%, in patients with gastric and duodenal ulcer - 66.7% and those with gastric ulcer - 59.6%. A positive correlation was observed between peptic ulcer incidence rates, complications of the disease and the value of the nicotinic index. The relationship between state of health and the value of the nicotinic index was confirmed. The results of the study showed that the nicotinic index was useful for determining the negative effect of cigarette smoking on the human body.