Methods of digestive endoscopy belong to the diagnostic standard of tumours of the digestive tract. The classical method is endoscopic examination of the upper and lower part of the tract which makes it possible to identify under visual control lesions which alter the character of the mucosal structure of hollow organs or lead to changes e.g. of the coloration of portions of the mucosa. From these sites samples can be taken to evaluate the character of the lesion and facilitate the differential diagnosis. Similarly examination of the pancreatobiliary system (ERCP) evaluates gross changes in the morphology of efferent systems. The objective is to find diagnostic methods which detect early stages of the disease, i.e. so-called minimal changes in the architectonics or biochemical structure at the level of the examined mucosa. These methods include endocopic sonography, supplemented by aimed biopsy. The examination makes it possible to visualize individual layers of the wall e.g. of the oesophagus, stomach or gut. An irregular pattern of the layers is the sign of a process which takes place inside the wall. New methods which make the diagnosis of mucosal lesions more accurate are endoscopic autofluorescence and optic coherent tomography (OCT). In particular OCT seems to be a promising contribution to the diagnosis of dysplasias and early tumourous changes of the oesophagus, stomach and gut.