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The separation of air-containing bowel loops on the supine plain film of the abdomen has, for many years, been an accepted radiographic sign of intraperitoneal fluid and more recently has been stressed as a sign of bowel wall thickening. While Nelson and Eggleston, in their excellent paper on mesenteric vascular occlusion, alluded to the possibility of intraluminal fluid giving the appearance of separated bowel loops, they offered no evidence or explanation. Intraluminal fluid can produce the appearance of abnormal separation of the walls of adjacent bowel loops. We will refer to this phenomenon as pseudo-separation. Our attention was directed to this sign when we encountered it frequently in patients having nonspecific abdominal pain. We even observed it in scout films of asymptomatic patients who showed anxiety concerning an impending examination such as intravenous urography, aortography, or gastrointestinal studies. Figure 1, A, demonstrates a case in which the scout film clearly shows “separation” of...