Endoscopy alone, without histology, has poor sensitivity and specificity for diagnosing diffuse mucosal diseases of the oesophagus, stomach and duodenum. Erosive lesions with exudate at the distal end of the oesophagus are a reliable sign of oesophagitis, but are present in only approximately 50% of patients with gastro-oesophageal reflux. Erythema and friability are unreliable and subject to considerable inter-observer variation. Numerous macroscopic abnormalities of the gastric and duodenal mucosa have been identified, but these show no consistent histological pattern.