Using the rapid pull-through technique the effect of oral 400 mg cimetidine on lower esophageal sphincter pressure was studied in a controlled trial in 14 subjects. Cimetidine caused a significant rise of the integrated basal pressure. The response to 0.6 .mu.g/kg pentagastrin was augmented by cimetidine; this effect could not be demonstrated under atropine sulfate infusion. Cimetidine may act on LESP by blocking inhibiting receptors.