Controversy exists over whether diazepam can be used for sedation during esophageal manometry studies without affecting the results. To evaluate the effect of diazepam, 20 healthy asymptomatic volunteers were studied using a standard manometry protocol employing an Arndorfer capillary infusion system. Following a baseline manometry, each subject received 0.1 mg/kg diazepam intravenously over 1 min and underwent repeat manometry 5 min after completion of the injection. All manometry recordings were coded and read blindly. The amplitude of the lower esophageal sphincter was significantly reduced by diazepam from 26.2 +/- 10.9 and 30.0 +/- 10.9 mm Hg to 18.8 +/- 7.6 and 24.5 +/- 9.7 mm Hg by rapid and station pull-through methods, respectively (P less than 0.01 both methods). Esophageal contraction wave duration was significantly increased following diazepam at 3, 8, and 13 cm above the lower esophageal sphincter (P less than 0.01 all levels). There was a trend toward increased contraction wave amplitude following diazepam administration in the lower three fourths of the esophagus. On the basis of these results, we conclude that diazepam sedation may produce misleading results when used during esophageal manometric testing. It is recommended that diazepam not be used in manometric studies of normal subjects or patients with reflux esophagitis and that manometric findings in patients with hypertensive or spastic disorders be interpreted with caution if diazepam is given as a premedication.