We determined the effect of increased bolus consistency on esophageal motor function in 11 healthy volunteer subjects. Further, we sought to define the esophageal response to boluses with a wide range of temperatures in nine healthy volunteers. Intraluminal pressure events were measured with an infused catheter system, and lower esophageal sphincter pressure was monitored continuously with a Dent sleeve. Boluses (10 swallows each) consisting of 5 ml of a solid suspension (yogurt), 5 cm3 of a soft solid (gelatin), and 5 ml of water were given in a randomized order. In a separate study, boluses with temperatures of 1 degree C, 5 degrees C, 10 degrees C, 15 degrees C, room temperature, 30 degrees C, 40 degrees C, 50 degrees C, and 60 degrees C were given in a randomized fashion. Compared to the water bolus, the solid boluses elicited a significant (P less than 0.05) reduction in peristaltic wave velocity, which was accompanied by significant (P less than 0.05) increments in the durations of wave contraction and lower esophageal sphincter relaxation. The magnitude of the response elicited by the solid boluses was comparable to that noted with boluses of high viscosity suggesting that the esophagus response to increments in bolus viscosity and consistency in a similar fashion. Alterations in bolus temperature did not elicit any significant changes in the parameters of esophageal peristalsis. It is concluded that bolus temperature does not have a significant role in the modulation of human esophageal peristalsis except under conditions that cause a change in esophageal wall temperature.