Survival rates of gastric cancer (GC) have been low, due to the fact that its diagnosis is often late and made in the advanced stage. The knowledge about the precursor lesions in development of gastric cancer could contribute to cancer diagnosis at an early stage. The biological development of GC in the gastric mucosa (GM) is characterized by the sequence: chronic inflammation-atrophic gastritis (AG)-dysplasia-GC. We aimed to investigate the function of oxidative phosphorylation (OXPHOS) in the GM cells in case of chronic gastritis, AG and GC and to find alterations, pointing to early pre-cancerous changes. Additionally, the energy transfer systems consist of adenylate kinase (AK) and creatine kinase (CK) intracellular and mitochondrial isoforms in case of chronic gastritis were studied. The results showed that: 1. In the human antrum and corpus GM exists AK and CK systems that are functionally coupled to OXPHOS. 2. In the atrophic corpus GM and in the GC cells oxidative capaciry is reduced and remodelling of the OXPHOS occurs, manifesting as deficiency of the complex I and improved function of the complex II. These changes may have a role in the development of gastric cancer.