We tested the hypothesis that short-chain fatty acids (SCFAs) and distention would stimulate ileal motility in humans. Intraluminal pressures in the ileocolonic region were recorded in 18 healthy human volunteers after instillation of boluses of SCFAs, air, and saline. Ileal motility was stimulated more often by SCFAs than by similar volumes of air or saline. Although increasing volumes of distention evoked greater numbers of contractions, this phenomenon was not apparent after repeated stimulation, suggesting that the "mechanoreceptor" in the human ileum has a refractory period. Symptoms of abdominal pain, cramps, and an urge to defecate may have resulted from instillation of SCFAs, even at small volumes. The motility stimulated in the ileum by SCFAs was not associated with systemic release of gastrointestinal regulatory peptides and was not affected by naloxone or indomethacin. Short-chain fatty acids, which can be considered as "markers" of colonic contents, might be associated with the motor response to coloileal reflux in humans.