The yield pressure at which the cardia opens in response to gastric distension was measured in 155 subjects with and without gastro-oesophageal reflux (GOR) and after Nissen fundoplication. Yield pressure was measured by endoscopy or during oesophageal manometry. The median pressure was significantly lower in subjects with GOR than in those without (P < 0.0001). After successful Nissen fundoplication this pressure increased to supranormal values (P < 0.0001). There was a close relationship between yield pressure and the presence and size of hiatus hernia and also between yield pressure and the valvular appearance of the cardia at endoscopy. There was a significant correlation between yield pressure and oesophageal acid exposure. However, no relationship was observed between yield pressure and lower oesophageal sphincter pressure or intra-abdominal length. These results suggest that yield pressure is useful for assessment of the competence of the cardia, particularly after antireflux surgery. The competence of the cardia is greatly influenced by its anatomical structure.