The purpose of this study was to develop a sonographic method to monitor postprandial size of the proximal stomach. Twenty-three healthy persons were scanned in a sitting position with a 3.25 MHz transducer after ingestion of 500 ml meat soup. The area in a sagittal section and the maximal diameter in an oblique frontal section were chosen as standard measurements. The soup emptied from the proximal stomach in a linear manner (r = 0.99) and at a rate of 2.0 +/- 1.3%/min. Intraobserver error of the scans (mean +/- SD) was 5.6% +/- 2.3% and 9.5% +/- 4.5% for sagittal area and frontal diameter, respectively, and the corresponding interobserver error was 5.3% +/- 4.0% and 8.3% +/- 5.3%, respectively. This sonographic method demonstrated a moderate day-to-day variation, had low intra- and interobserver error, and allowed estimation of initial emptying fractions of the proximal stomach.