Acute intestinal distention in dogs induces a gastric relaxatory reflex. Our aim was to investigate this reflex in humans, including its relationship to perception. In 9 fasting healthy volunteers, we performed graded balloon distentions (2.5 min duration at 10-min intervals) of either the antroduodenal junction (n = 6) or the distal duodenum (n = 6). Gastric tone was quantified as changes in the volume of air within an intragastric bag maintained at a constant pressure by an electronic barostat. Perception was scored by a graded (0-6) questionnaire. Distention of the antroduodenal junction induced dose-related gastric relaxatory responses: distention at a level producing significant perception (5.0 +/- 0.1 perception score) induced significant relaxation (203 +/- 39 ml change in intragastric volume; p less than 0.05); lower levels of distention still induced relaxation (113 +/- 30 ml change in volume; p less than 0.05) without significant perception (1.0 +/- 0.5 perception score). In the distal duodenum, distention at the threshold for discomfort (5.1 +/- 0.3 perception score) induced significantly smaller gastric relaxatory responses (42 +/- 17 ml change in volume). Distentions below the level of significant perception (1.5 +/- 0.7 perception score) failed to induce gastric responses (14 +/- 15 ml change in volume). These data indicate that both perceived and unperceived gastric relaxatory reflexes in response to distention exist in humans and that these reflexes are region dependent.