Antroduodenal motility, pH and gastric emptying rate were measured in 11 patients undergoing orthopaedic or plastic surgery with general anaesthesia. Motility was measured by manometry and gastric emptying rate by the rate of paracetamol absorption. During anaesthesia, gastric emptying was delayed in eight patients. General anaesthesia with halothane reduced the duration of the interdigestive motility complex (P less than 0.01), mainly by a shortening of phase II (P less than 0.01) which correlated with the inhaled concentrations of halothane (P less than 0.01). Anaesthesia impeded the occurrence of antral contractions during phase II (P less than 0.01); the frequency of contractions was unchanged during anaesthesia, but decreased during the recovery period (P less than 0.01). The amplitudes of antral contractions diminished with anaesthesia (P less than 0.01), but increased after operation. The frequency of contractions in the duodenum was unchanged during phase II and reduced during phase III (P less than 0.01). Gastric pH increased during and after operation (P less than 0.01). General anaesthesia with halothane affects gastroduodenal motility especially during phase II, increases gastric pH and delays gastric emptying rate.