The gastric emptying of liquids is determined by the pressure gradient between the stomach and the duodenum. This study monitored intragastric and intraduodenal pressures of 7 healthy volunteers during the gastric emptying of an acid meal (pH 2) and an oleate meal (50 mM) in comparison with the gastric emptying of a 154 mM saline meal (pH 7) in order to elucidate the mechanisms of delayed gastric emptying seen with the acid and the fatty meals. Antroduodenal motility was measured by means of a continuously perfused catheter system, and fundic pressure was monitored by means of a water-filled balloon. Gastric emptying was measured with the double sampling dye dilution technique. As expected, the gastric emptying of the pH 7 meal (t 1/2 = 2.2 +/- 0.7 min) was significantly faster than that of the acid (t 1/2 = 11 +/- 2.1 min) and the oleate (t 1/2 = 18 +/- 2 min) meals. The rapid gastric emptying of the neutral meal was consistently associated with a significant increase in tonic fundic pressure (p less than 0.05), a feature never seen with the acid and the oleate meals. There was no change in duodenal motility with the gastric emptying of the neutral meal, whereas duodenal activity did tend to increase with the acid and oleate meals. Thus the proximal stomach appears to be the main determinant of variations in the gastric emptying of liquids, whereas the duodenum appears to have a less prominent role.