Protein tyrosine kinase (PTK) cascades, regulated by oxygen and nitrogen reactive species, play an important role in reepithelisation of gastric mucosa after lesions (Tarnawski, 2005,Dig Dis Sci, 50, 24–33). Wistar rats were subjected to cold stress (Biswas, 2003, J Biol Chem, 278, 10993-11001) to provoke stomach lesions. Activities of PTKs and protein tyrosine phosphatases (PTPs) were measured using Sigma-Aldrich Assay Kits. Standard methods were used to evaluate other parameters. The data were expressed as means ± S.E, n=6. The significance was calculated using One-Way ANOVA and t-test in STATISTICA 5.0. Acute cold stress decreased the activities of PTKs and PTPs in gastric mucosa (GM) cells. Superoxide dismutase (SOD) activity did not change, catalase activity increased slightly, glutathione peroxidase (GP) was inhibited 2.3 fold, hydroxyl radical (OH•) content increased 3.3 fold, zinc content decreased 2.3 fold, and nitric oxide synthase (NOS) activity increased three times. Recently it was discovered that gastric proton pump inhibitors, omeprazole and its analogues, had additional effects on GM cells (Blandizzi, 2005, World J Gastroenterol, 11, 4052-4060).; Biswas, 2003). Omeprazole treatment (0.8 mg/kg i.p.) after cold stress restored PTK and PTP activities in GM cells to normal, increased SOD activity and OH• content, inhibited catalase and GP and decreased zinc content without activating NOS. In unstressed animals treated with the drug, inhibition of non-receptor PTK and PTP was accompanied by activation of GP and NOS. The data confirm that omeprazole treatment has different effects on enzymatic activity in GM cells of stressed and unstressed animals.