The diagnosis may be obvious with the finding of hematemesis, hematochezia, or melena. A careful ear, nose, and throat (ENT) examination can exclude swallowed blood as a source. Nasogastric (NG) tube placement and aspiration may detect occult upper GI bleeding. A negative NG aspirate does not conclusively exclude an upper GI source. Guaiac testing of NG aspirate can yield both false-negative and false-positive results. Most reliable is gross inspection of the aspirate for a bloody, maroon, or coffee-ground appearance, reserving guaiac testing to confirm that what appears to be blood actually is. A rectal examination is mandatory to detect the presence of blood, its appearance (bright red, maroon, or melanotic), and the presence of masses. All patients with significant GI bleeding require type and crossmatch for blood. Other important tests include a complete blood count, electrolytes, blood urea nitrogen, creatinine, glucose, coagulation studies, and liver function tests. The initial hematocrit level may not reflect the actual amount of blood loss. Upper GI bleeding may elevate the blood urea nitrogen level. Routine abdominal radiographs are of limited value. Controversy remains as to whether angiography, scintigraphy, colonoscopy, or multidetector CT and in which order, is initial diagnostic procedure in the evaluation of lower GI bleeding.