Recently, 24-h recording of intraesophageal pH and pressure signals in ambulatory subjects has become possible. Several research applications of the technique have emerged, but until now only a few clinical applications have been established, the most important of which is noncardiac chest pain. In the computer analysis of the signals, the patient with noncardiac chest pain is used as his or her own control; motility and pH profiles during pain are compared with asymptomatic base-line values obtained from the same patient. Automated analysis by means of a computer avoids observer bias and saves time. By means of 24-h monitoring, motor abnormalities have been identified as the cause of the chest pain in 4.5% to 18% and reflux in 4.5% to 25% of the patients studied. In addition, patients were identified who have both dysmotility- and reflux-related pain episodes. The yield of 24-h monitoring is highest in patients who have frequent pain episodes. A high yield of 24-h monitoring was found in patients with noncardiac chest pain admitted to a coronary care unit. Seventy-six per cent of these patients were found to have either reflux- of dysmotility-related chest pain. Patients with proven coronary artery disease who do not respond well to adequate treatment frequently have gastroesophageal reflux (39%) or esophageal motor abnormalities (50%) as the cause of their ongoing pain attacks. In these patients, identification of the esophageal cause of the symptoms not only helps the physician to select the optimal treatment but also reduces the patient's need for medical care.