The body possesses many various endogenous substances that enable it to protect itself from various noxious events. One of the nonspecific reactions is the increase of endogenous zinc concentrations in various tissues. The aim of this study was to focus on the changes of zinc serum and tissue concentrations in well-established models of gastric (24 h restraint stress and 5 min ethanol) and duodenal ulceration (24 h cysteamine). Ten female Wistar rats, weighing 180-250 g were used in each of the experimental groups. Upon sacrificing, the ulcer index was recorded. Zinc serum and tissue concentrations were determined using atomic absorption spectrophotometry. Ten unstressed animals served as a healthy control group. The results of our study clearly indicated certain changes in serum zinc in all these ulcer models. Changes in tissue concentrations, varying from model to model, were also observed. In conclusion, all this data confirm the fact that endogenous zinc represents a natural line of the body's defense system when exposed to stress.