To investigate the effect of bethanechol on postprandial gastroesophageal reflux in children, and the relationship between its effect on the lower esophageal sphincter pressure and its effect on reflux, we studied 31 consecutive children with pathologic reflux, using manometry and pH probe, both before and after administration of bethanechol. The initial sphincter pressure was subnormal in only 35% of the patients. The bethanechol-treated sphincter pressure was increased in 97% of the patients (from 13.4 +/- 1.3 to 34.1 +/- 2.6 mm Hg) and was normal in 97% of the patients, yet bethanechol did not improve any measure of postprandial reflux in the patient group as a whole. Furthermore, the 20 patients with normal sphincter pressures had significant worsening of their percent of postprandial time with reflux (from 21.8 +/- 5.3 to 33.8 +/- 6.0%, p = 0.009). Thus, this study demonstrates a failure of the acute administration of bethanechol to improve postprandial gastroesophageal reflux and raises the issue of whether the widespread use of bethanechol to treat reflux in children is appropriate.