A bloody nasogastric aspirate is believed to imply active upper gastrointestinal tract bleeding, while a nonbloody yellow-green nasogastric aspirate that contains duodenal secretions suggests the absence of bleeding proximal to the ligament of Treitz. To validate these beliefs, physicians were asked to predict the presence of active gastrointestinal tract bleeding and whether bile was present in a nasogastric aspirate obtained immediately before endoscopy in 73 episodes of bleeding in 62 patients. A relationship was found between the physician's assessment of the presence of active bleeding demonstrated endoscopically and the appearance of the nasogastric aspirate. However, the sensitivity and specificity were low (79% and 55%, respectively). No association between the assessment of bile in the nasogastric aspirate and the presence of bile acids was demonstrated. These data do not support the placement of a nasogastric tube to determine whether or not a patient is bleeding, the location of the bleeding, and whether endoscopy should be performed.