Gastric tone may mediate gastric accommodation and emptying; however, it cannot be recorded by manometric methods. We have developed an electronic barostat that maintains a constant pressure (2 mmHg) within an air-filled bag and have validated the system in vitro and in vivo. In four conscious dogs, the bag was introduced orally into the stomach, and gastric tone was monitored from the barostat as variations in intrabag volume. Simultaneously, we recorded upper gut pressure activity by implanting manometric catheters. Studies were performed in fasting and fed (200-ml solid meal) dogs. The barostat system did not distort fasting motor activity. Intrabag volume correlated with manometrically measured fundic pressure activity. However, tonic changes undetected manometrically were clearly registered by the barostat. Meal induced marked changes in gastric tone. A receptive relaxation during feeding was followed by a low-tone accommodation period. Later, the barostat registered a sustained high tone until the return of the fasting pattern. We conclude that the electronic barostat measures physiological variations in gastric tone that are not recorded by conventional systems.