The effect of a gastrointestinal tube on the passage of a radiolabeled solid meal through the stomach and small intestine was investigated in 22 healthy volunteers using the gamma camera and breath hydrogen analysis. Gastric emptying was significantly retarded in 12 subjects, who had an intestinal tube in situ compared with 10 control subjects, who were not intubated (t 1/2 = 1.5 +/- 0.1 vs. 1.2 +/- 0.1 h; p less than 0.02). On the other hand, colonic filling was significantly accelerated in the intubated subjects (onset: 1.2 +/- 0.2 vs. 2.9 +/- 0.4 h; p less than 0.001; t 1/2: 4.1 +/- 0.3 vs. 5.6 +/- 0.5 h; p less than 0.001). Values for small bowel residence were significantly reduced in the intubated subjects (5.3 +/- 0.5 vs. 6.5 +/- 0.6 food hours; p less than 0.001). Paired studies, carried out in an additional 11 normal subjects, confirmed that small bowel transit time was significantly shortened during intestinal intubation in the same individuals (2.0 +/- 0.3 vs. 3.6 +/- 0.4 h). These results suggest that intubating the gastrointestinal tract may profoundly affect its function.