Gastric mucosa and blood plasm were studied in 82 patients with gastroduodenal ulcer for content of adenylic nucleotides (AMP, ADP and ATP), histamine, amino acids. It was found that the above nucleotides occurred in the examinees in subnormal quantities. The necessary substrates, aspartate in particular, were deficient. This may lead to impairment of biosynthetic processes, to imbalance of defense factors. Photon therapy of gastroduodenal ulcer corrects bioenergetic metabolism in gastric mucosa thus producing a marked therapeutic effect.