1. In the conscious calf it is possible to use duodenal re-entrant cannulae to measure the output of a gastric test meal directly from the proximal cannula placed near the pylorus. At the same time the duodenum can be isolated from the stomach and maintained under constant stimulus by a continual infusion at regulated pressure, volume and temperature into the distal cannula. 2. Under these experimental conditions the pattern of gastric emptying is exponential in form. Thus direct recording of gastric emptying validates indirect methods, such as the serial test meal, where volume markers are used. It appears likely that the exponential pattern of gastric emptying is common to man, dog, cat and calf. 3. When the isolated duodenum was infused with water, the exponential pattern of gastric emptying was maintained even when the volume of meal instilled was increased substantially from 1 to 41. 4. Distension of the stomach by larger test meals did not affect the relative rate of emptying so that the half-time of emptying of all meals was about the same. 5. When the isolated duodenum was infused with 0-06 M-HCl gastric emptying of the smaller meals was almost completely inhibited. The inhibition of gastric evacuation was accompanied by inhibition of the gastric e.m.g. 6. Infusion of the duodenum with acid also produced marked, but not complete, inhibition of emptying the larger test meals but the distension produced by the larger meals appeared to partially overcome the inhibitory effect of the acid duodenal infusate so that a small efflux occurred from the stomach. This small efflux was usually associated with some slight degree of gastric e.m.g. activity. 7. We are still investigating the mechanisms whereby the duodenum affects gastric emptying, but it is clearly demonstrable from our present results that the inhibitory effects of acid duodenal infusate are sufficiently powerful to overcome the forces, both physical and reflex, which normally aid gastric evacuation.