The accuracy of endoscopy and directed biopsy in the differential diagnosis of gastric lesions was evaluated by comparing the diagnoses of one endoscopic procedure (endoscopy and multiple directed biopsies) with the definitive diagnoses in 333 patients. The overall endoscopic and bioptic accuracy rate for all patients amounted to 98.8%. Separate accuracy rates of endoscopy alone and biopsy were 86.5% and 94.9%, respectively. The reliability of endoscopy was similar in the diagnosis of malignant and benign lesions (86% and 89%). Endoscopic biopsy was correct in 99.1+ of benign lesions and in 86% of malignancies. False negative rates were 3.9% for endoscopy and 4.0% for biopsy. It is concluded that one endoscopic procedure is a highly reliable method in the differential diagnosis of benign and malignant gastric lesions.