The gastric acid secretion in the awake state of the pig was compared to that during halothane, chloralose, pentobarbital and etomidate anaesthesia. After collection of basal juice, acid secretion was stimulated with pentagastrin in the dosages of 0.25, 1.00 and 4.00 µg/kg/h. Halothane strongly inhibited acid secretion, whereas acid secretion during chloralose anaesthesia was enlarged by a factor 6 as compared to that of the awake animal. The mean acid output after receiving pentobarbital was close to that of the awake condition, but the interindividual variation was large. Nearly identical values for acid secretion were found during etomidate anaesthesia, but with much higher consistency in the results. Etomidate anaesthesia seems to be the most suitable method for measurements of gastric acid secretion during anaesthesia in the pig.