The results of endoscopic ultrasonography in the diagnosis and differentiation of benign and malignant lesions of the stomach was prospectively compared with those obtained by upper endoscopy with biopsy, double-contrast radiography and computed tomography in 15 patients with benign and 26 with malignant gastric lesions. The validity of the methods was established by comparing the results obtained with the long-term course observed clinically in conjunction with an endoscopic-histological follow-up or with the findings on histopathological examination of the operative specimen. Precise diagnosis of the lesion was made by endoscopic ultrasonography in about 90% of cases, a result better than that obtained with radiography or computed tomography. Furthermore, endoscopic ultrasonography had good sensitivity for demonstrating perigastric lymph node enlargement; in this respect it was better than computed tomography, but was not able to distinguish whether the enlargement was benign or malignant: this will only become possible with technical improvement of the instruments.