A safe non-invasive technique for the measurement of gastric volume by real-time ultrasound is described. The application of this technique to the measurement of the emptying of liquid from the stomach is outlined. Gastric emptying of liquid was found to be log-linear, the mean half-life of emptying in 10 volunteers being 22 . 0 +/- 2 . 5 min. Ultrasound measurement of gastric emptying provides an opportunity to study the effects of drugs and disease on gastric motor function in man.