In 95 per cent of patients, the source of gastrointestinal bleeding can be determined by the usual roentgenographic and endoscopic methods. In the remaining five per cent of patients, the source of bleeding is obscure and special diagnostic procedures will be necessary. Among the special procedures that have been reported are the fluorescein string test, stepwise aspiration of intestinal contents, detection of radioactive red blood cells by stepwise aspiration, Geiger counter or scanning, and selective visceral angiography. An additional procedure, reported here, combines exploratory celiotomy with total endoscopic examination of the bowel.