Biomechanical wall properties of the human esophagus were studied. A probe, with a balloon designed for simultaneous measurement of cross-sectional area and intraluminal pressure, was placed in the esophagus 30 cm from the incisors. Tone was not detected before inflation of the balloon. When the balloon was inflated stepwise with pressures up to 40 cm H2O (30.7 mmHg), measurement of cross-sectional area allowed calculation of distensibility and circumferential wall tension. Balloon cross-sectional area increased linearly with increased balloon pressure. Balloon distension induced contractions, both proximal to the balloon and at the site of distension, at a balloon pressure of about 15 cm H2O (11.5 mm Hg). The cross-sectional area for the threshold for distension induced contractions was 153 +/- 12 mm2 (diameter 14 mm). At the onset of these contractions, the contraction force was 15-20 cm H2O (11.5-15.3 mm Hg) and it increased to 47-58 cm H2O (36.1-44 mm Hg) at a balloon pressure of 20-40 cm H2O (15.3-30.7 mm Hg). Circumferential wall tension increased with increasing intraluminal pressure in an almost exponential manner. The pressure elastic modulus increased steeply at lower balloon pressures (10-20 cm H2O) (7.7-11.5 mm Hg), but at higher balloon pressures (20-40 cm H2O) (15.3-30.7 mm Hg) this increase was less. The circumferential wall tension and wall stiffness of the human esophagus increased with increasing balloon pressure and cross-sectional area. When a threshold is reached, distension induced contractions both proximal and distal to the balloon and at the distension site.