The effects of diazepam on antroduodenal motility, gastric pH and gastric emptying rate were investigated in 10 volunteers. Gastric emptying was assessed using paracetamol absorption and antroduodenal motility and pH by means of a perfused multilumen tube. On the first study day, the volunteers received paracetamol in phase I after the occurrence of one complete interdigestive motility complex (IDMC). Diazepam was given on the second study day at the beginning of the first phase I and paracetamol was given one IDMC later. The rate of absorption correlated with motility (P less than 0.03). Some volunteers were fast absorbers on the first study day and slow on the second, indicating that absorption rate is not constant, but dependent on gastroduodenal motility. Diazepam tended to increase the gastric emptying rate and enhanced the amplitude of contractions and the motility index during phase II (P less than 0.02). Gastric pH increased after ingestion of diazepam (P less than 0.05).