Understanding of the control mechanisms underlying gastric motor function is still limited. The aim of the present study was to evaluate antral pressure-geometry relationships during gastric emptying slowed by intraduodenal nutrient infusion and enhanced by erythromycin. In seven healthy subjects, antral contractile activity was assessed by combined dynamic magnetic resonance imaging and antroduodenal high-resolution manometry. After intragastric administration of a 20% glucose solution (750 ml), gastric motility and emptying were recorded during intraduodenal nutrient infusion alone and, subsequently, combined with intravenous erythromycin. Before erythromycin, contraction waves were antegrade (propagation speed: 2.7 ± 1.7 mm/s; lumen occlusion: 47 ± 14%). Eighty-two percent (51/62) of contraction waves were detected manometrically. Fifty-four percent of contractile events (254/473) were associated with a detectable pressure event. Pressure and the degree of lumen occlusion were only weakly correlated (r² = 0.02; P = 0.026). After erythromycin, episodes of strong antroduodenal contractions were observed. In conclusion, antral contractions alone do not reliably predict gastric emptying. Erythromycin induces strong antroduodenal contractions not necessarily associated with fast emptying. Finally, manometry reliably detects ~80% of contraction waves, but conclusions from manometry regarding actual contractile activity must be made with care.