The present study was undertaken to determine the onset and duration of gastric acid stimulation by amino acids measured by continuous intragastric pH-monitoring. A 3-hour intravenous infusion of 250 ml of an amino acid solution (Vamin 18) was given to 20 healthy volunteers. The results were compared with data obtained during basal conditions and during a 3-hour intravenous infusion of a 5% glucose solution. One hour after starting the amino acid infusion the decrease in intragastric pH-levels reached statistical significance (p less than 0.02). This increased intragastric acidity lasted for one hour after stopping the amino acid infusion. Serum gastrin levels remained unchanged. These results indicate that continuous intragastric pH-monitoring is capable of demonstrating stimulation of gastric acidity during and for one hour after an amino acid infusion. These findings may be important for patients on parenteral nutrition.