Endoscopic ultrasonotomography opens a sonographic window to the organs of the mediastinum. With this technique all segments of the oesophagus can be sonographically investigated. Endosonographic investigations on 11 patients with oesophageal tumors and 3 patients with oesophageal varices showed that the diagnosis of oesophageal carcinoma and differentiation between malignant tumors and benign changes are possible. The spread of the tumor in the horizontal and vertical planes can be accurately determined with endoscopic ultrasonography. In addition, paraoesophageal lymph node metastases, as well as other lesions in the mediastinum, can be diagnosed. Ultrasonography of the oesophagus can be simplified by leaving out the optical system.