Abstract Experiments were conducted to determine to what extent the duodenum resists the emptying of various solutions from the isolated stomach. Cat stomachs were maintained in Krebs solution In vitro, and filled with 100 ml isotonic saline solution, isotonic glucose, hypertonic saline solution, hypertonic glucose, or dilute acid. Gastric pressure was constantly monitored; gastric output was collected constantly by a cannula In the proximal or distal duodenum. For all solutions, cumulative gastric output at all times was considerably less with the distal than the proximal cannula position. This difference was almost entirely caused by a smaller fractional gastric output during the first minute of gastric emptying, and by reduced amplitude of the gastric stroke volume with the distal cannula position. Some differences were observed In the gastric emptying rate for the various solutions; Isotonic saline solution emptied particularly slowly and hydrochloric acid emptied particularly fast. In addition, the various solutions produced different gastric pressure patterns, which could not be entirely explained by differences in residual gastric volume. We concluded that the cat duodenum provides a resistance to gastric emptying over and above that generated by the pylorus, and that the duodenal resistance is caused by limitations In duodenal capacity. It is furthermore concluded that the mechanical activity of the isolated stomach and duodenum is affected by the chemical composition of their luminal contents.