In a double-blind study the gastro-oesophageal sphincter pressure profile was measured in a group of twenty women in the last trimester of pregnancy, all of whom suffered from heartburn. The mean gastric and the maximum sphincter pressures were calculated from the pressure profile, and the difference between these two was defined as the barrier pressure. After resting sphincter measurement ten of the women were given 10 mg metocolopramide intravenously, and the other ten had a placebo intravenous injection; 15 min later the sphincter pressures were measured again. Metoclopramide significantly increased the mean maximum sphincter and barrier pressures compared to the baseline pressure, and there was no significant difference between the pre- and post-injection pressures in the placebo group. However, the raised mean maximum sphincter and barrier pressures following metoclopramide were made up of four patients having very high pressures and six patients on whom metoclopramine appeared to have little effect. The clinical usefulness of metoclopramide in women in labour is discussed.