ABSRACT 59 patients with stomach diseases including gastric cancer or poiyp, gastritis, esofagus disease were investigated. Before gastroscopy all patients were given 5-ALA in doses 5mg, 10mg and 20mg per 1kg ofbody weight orally. Fluorescence diagnostics (FD) which estimates concentration of ALA-induced PPIX in regular and alternated tissues of gastric mucosa were carried out in 2-4 hours. Using of 5-ALA hs shown high diagnostic effectiveness for differential diagnostics of stomach diseases. This technique has proved 1 0 diagnosis of cancer and revealed 1 5 malignant stomach diseases including 4 cancer in situ for patients with preliminary diagnosis of gastric ulcer. It also revealed 5 patients with enhanced fluorescence for which aimed biopcy has shown high degree of inflammation process. The latter were assigned as a risk group.