BACKGROUND/AIMS: Primary esophageal motility disorders (achalasia, diffuse esophageal spasm, and intermediate forms) are suggested to be caused by different degrees of inhibitory dysfunction; however, direct evidence for this hypothesis has never been presented in humans. The aim of this study was to measure the degree of inhibition that precedes deglutitive contractions in patients with primary motility disorders. METHODS: Deglutitive inhibition was examined in patients with primary motility disorders: 9 with achalasia, 6 with symptomatic diffuse esophageal spasm, and 5 with intermediate forms. An artificial high-pressure zone was created in the esophageal body by inflating a balloon to a critical level, and pressure changes were measured at the interface between the balloon and esophageal wall. Inhibition was visualized as a relaxation of the artificial high-pressure zone. RESULTS: An inverse relationship was found between the degree of inhibition and the propagation velocity of the deglutitive contraction (r = 0.75; P < 0.001). Normally propagated contractions were preceded by an inhibition of 84.2% +/- 3.6%; fast-propagating contractions were preceded by partial inhibition of 40.6% +/- 6.2%; and, in case of simultaneous contractions, inhibition was absent, i.e., 2.6% +/- 1.6%. CONCLUSIONS: The spectrum of primary motility disorders is an expression of a progressively failing deglutitive inhibition.