Many studies have been reported indicating that the contents of the stomach and small intestine influence the appearance of administered barium sulfate suspensions (1, 5, 9). This depends on the type of barium suspension used: plain barium sulfate versus preparations containing suspending agents. Frazer et al. (9) demonstrated that in normal subjects hypertonic solutions and long-chain and certain short-chain fatty acids cause a segmentation pattern in the small bowel apparently secondary to increased mucin secretion stimulated by these substances. Chang and Carroll (6) described marked mottling and flocculation of barium in the stomach in patients with hyperacidity and a frothy, foamy, and bubbly appearance in those with hypoacidity. Bryk and Robinson (4) showed that, in pyloric obstruction due to duodenal ulcer, hypersecretion and hyperacidity lead to precipitation and layering of barium while in neoplastic obstruction with its associated hypoacidity precipitation and layering are less common. Knoefel et al. (13) performed in vitro studies which indicated that the precipitation of barium was related to the volume and acidity of the gastric juice and its mucoprotein content. In the small bowel abnormal patterns have been described with duodenal ulcer (2), the Zollinger-Ellison syndrome (7, 15, 22), the malabsorption syndrome (5, 19), and a large number of other conditions which alter the bowel contents (2). These studies have indicated that the abnormalities noted are most prominent with plain barium sulfate suspensions and are completely or almost completely eliminated with the use of barium suspensions containing suspending agents. In duodenal ulcer and in the Zollinger-Ellison syndrome, it was postulated that the abnormalities were due to the large volume and the low pH of the gastric contents presented to the small bowel. A study in dogs (17) showed that instillation of 0.1 N HCl into the stomach increased the fluid volume of the ileum, increased its free acid content, and produced diarrhea. Multiple studies have been reported on the effect of administered acid or alkali on gastric emptying. These have generally agreed that in most normal adults acid solutions delay gastric emptying while isotonic solutions of alkali hasten emptying (11, 12, 18, 21). No studies, however, have been done on the roentgenographic gastric, duodenal, and small bowel patterns resulting from the use of barium sulfate suspensions whose pH has been adjusted to the equivalent of either the gastric or the duodenal contents. Acid barium (pH 1.7) has been recently described (8) as useful in evaluating clinical esophagitis, but its effect on the remainder of the gastrointestinal tract has not been described. No studies on the roentgenographic patterns produced by alkaline barium suspensions are available.