Our aim was to measure axial forces in the stomach and to evaluate their relation to circumferential contractions of the gastric walls and the emptying of gastric content. We used a combination of simultaneous radioscintigraphy, gastroduodenal manometry, and an axial force transducer with an inflatable 2-ml balloon fluoroscopically placed in the antrum. In vitro studies demonstrated that the axial force transducer records only antegrade forces along the longitudinal axis of this probe in an intensity-dependent manner. In vivo studies were performed in five healthy subjects for at least 3 h after ingestion of radiolabeled meals. When administered separately, the emptying of liquids or solids from the stomach is associated with generation of antral axial forces and coincident phasic pressure activity; however, almost 20% (average) of gastric axial forces during emptying of liquids or solids are unassociated with proximal or distal antral pressure activity ("isolated" forces). High amplitude antral axial forces and pressures occur during both lag and postlag emptying phases. During emptying of liquids, there is a trend for axial forces to be coincident more often with proximal than with distal antral pressure activity and vice versa for the emptying of solids (P = 0.015). These data suggest that when placed in the antrum, the transducer can semiquantitatively record axial forces during gastric emptying. By combining these observations with the data from in vitro studies, it appears that axial forces predominantly result from traction on the balloon by the longitudinal vector resulting from circumferential gastric contractions. The combination of radioscintigraphy and measurement of antral axial forces is a promising method to evaluate mechanical forces involved in the emptying of the human stomach.