LES pressure increase following diaphragmatic contraction as a pinch-cock action acts as one of the barrier mechanism for gastroesophageal reflux. In achalasia patients, incomplete LES relaxation following wet swallow is one of the characteristic manometric findings, along with loss of peristalsis. On the other hand, it has been reported that swallowing effort or esophageal distention have no effect on the increase of LES pressure induced by diaphragmatic contraction, which condition is similar to achalasia. Therefore, to evaluate that whether diaphragmatic contraction is involved in the cause of achalasia, we recorded diaphragmatic electromyography (DEMG) using bipolar electrodes in 12 achalasia patients and 4 normal subjects. The phasic DEMG amplitude was 80-90 microV in normal subjects and achalasia patients. LES pressure and DEMG amplitude increased during both straight leg raising (SLR) and abdominal distention (AD), both of the maneuver induce diaphragmatic contraction, in normal subjects and achalasia patients similarly. From the data obtained with this equipment, we conclude that diaphragmatic involvement is not likely as a pathogenesis of LES dysfunction in achalasia patients.