The delivery of dextrose solutions to the duodenum is associated with the stimulation of phasic and tonic pyloric contraction. In this study, the effects of intravenous atropine on the antropyloroduodenal motor responses to intraduodenal infusions of 25% dextrose were assessed in 10 normal volunteers. Antropyloroduodenal pressures were recorded with a manometric assembly incorporating a sleeve sensor spanning the pylorus, and sideholes in the antrum and duodenum. In each experiment, three intraduodenal infusions of 25% dextrose were given at a rate of 4 ml/min, for a median duration of 19 min (range 17-20). During the second dextrose infusion, intravenous atropine was given as a bolus (15 micrograms/kg) followed by an infusion (4 micrograms/kg.min), which was continued until the end of each experiment. Before atropine was given, the pyloric motor response to the second dextrose infusion was not significantly different from the response to the first infusion, but after administration of atropine there was a rapid decrease in the rate of isolated pyloric pressure waves, from 0.8 to 0.1 per minute (p less than 0.05). The isolated pyloric pressure wave response to the third dextrose infusion was completely blocked, and there was a much smaller maximum increase in basal pyloric pressure compared with the first infusion (p less than 0.01). This study indicates that intraduodenal dextrose reproducibly stimulates isolated pyloric pressure waves and increases basal pyloric pressure by mechanisms that involve muscarinic receptors.