THE clinical diagnosis of duodenal ulcer seems to have been revolutionized by advances in technology, particularly by the development of the fiber-endoscope during the past few years. Yet many questions still need to be asked. In many ways, to consider the clinical diagnosis of duodenal ulcer is to wander in the wiles of epistemology. How do we know? What do we know? Is the matter of duodenal ulcer and its pain simply solipsistic, pain being all that counts, or must we see the ulcer to know that it is there? Is there a different outlook for the patient with duodenal-ulcer . . .