The entire small bowel can be visualized on ultrasonography after ingestion of nonabsorbable, isosmotic polyethylene glycol electrolyte balanced oral solution, termed small intestine contrast ultrasonography. The aims of this study were to assess whether the ingestion of different volumes of sonographic contrast solution may differently affect (1) small bowel distention and thus its sonographic appearance and (2) the time to visualize the entire small intestine. An additional aim was to identify the minimal amount of contrast solution necessary to visualize the entire small bowel. An ultrasonographic examination of the abdomen was performed twice in six healthy subjects after the ingestion of the isosmotic polyethylene glycol solution. During the first investigation each subject was asked to drink increasing amounts of sonographic contrast solution until the jejunum was visualized at ultrasonography. During the second investigation each subject was asked to drink increasing amounts of sonographic contrast solution, not to exceed a total volume of 260 ml. At the first examination the entire small bowel was visualized 39.3 +/- 17 min after ingestion of 647 +/- 105 ml of contrast solution. At the second examination the entire small bowel was visualized 43.5 +/- 13.5 min (not significant with respect to the first study) after the ingestion of 239 +/- 32 ml of contrast solution (P < 0.01 versus the first study). The mean luminal diameter and wall thickness at three intestinal levels did not differ in the two studies and were not statistically related to the amount of ingested sonographic contrast solution. Loose stools were the only side effect and were reported after the ingestion of more than 600 ml. Ultrasonography offers reproducible information on the morphology of the contrast agent-filled small bowel after ingestion of a wide range of volumes (175 to 820 ml) of isosmotic polyethylene glycol electrolyte balanced solution. On average, the entire small intestine could be visualized on ultrasonography by about 45 min after the ingestion of 600 ml or less of contrast solution without any side effects.