The aim of this study was to test the hypothesis that, under physiologic conditions, the human small bowel discriminates between the solid and aqueous components of chyme, that is, that in a fashion analogous to the stomach, the intestine would allow the liquid fraction to progress at a faster rate than solid particles. To evaluate this hypothesis, we took advantage of a gamma-emitting solid marker, 131I-fiber, previously developed in our laboratory, that is recognized by the stomach as a solid and that is emptied at a slower rate than liquid markers. Thus, 131I-fiber enters the intestine during feeding at a slower rate than a liquid marker, being eventually excreted in the feces physically and chemically unchanged. We also developed a mathematical method to calculate the intestinal transit spectrum based on scintigraphic data obtained from 6 healthy individuals who ingested 131I-fiber and technetium 99m (99mTc)-diethylenetriaminepentaacetic acid (DTPA)-water with a meal. The results disprove the hypothesis by showing that whereas 131I-fiber, as expected, leaves the stomach at a much slower rate than 99mTc-DTPA-water, both markers progress along the small bowel separately but at similar speeds. Our method for measuring intestinal transit provides a more comprehensive quantification of chyme transit in the human small bowel than earlier methods and should prove a useful technique for further noninvasive studies of transit after feeding.