Fibre-optic instruments have been used on 212 occasions to examine 177 patients who were symptomatic after peptic ulcer surgery. A diagnosis other than gastritis was reached in 83 patients, including 46 ulcers. Five ulcers were not seen–4 as a result of using inadequate equipment early in the series. Radiology detected only 60 per cent of the ulcers and raised many false-positive diagnoses. Expert review of the radiographs corrected many originally mistaken interpretations. Retained suture materials were seen by endoscopy and removed using biopsy forceps. Gastric mucosal congestion and gastritis were common in the operated stomach, but the clinical significance of these changes remains obscure in the absence of a control series. Fibre-optic endoscopy is now an essential part of the investigation of patients who are symptomatic following ulcer surgery.