Sixteen non-selected patients undergoing endoscopic cholangiopancreatography (ERCP) after diazepam premedication were monitored for oxygen saturation (SpO2) with a pulse oximeter and for myocardial ischaemia with a Holter tape recorder from 2 h before ERCP to 6 h after the procedure. One patient was excluded from data analysis because of oxygen therapy. Oxygen saturation was significantly decreased (p less than 0.05) both during endoscopy and in the postendoscopy recovery period. Heart rate was significantly increased (p less than 0.05) both during and after the procedure. ST depression occurred in no patients before endoscopy, in 10 patients during, and in no patients after endoscopy. Concurrent ischaemia and episodic hypoxaemia were found in 5 patients, isolated ischaemia in 7 patients, and isolated episodic hypoxaemia in 13 patients. Concurrent ischaemia and tachycardia were found in 10 patients, ischaemia without tachycardia in no patients, and isolated tachycardia in 1 patient. There was no significant correlation between diazepam dose and SpO2 during endoscopy. These results suggest tachycardia to be more important than hypoxaemia in the pathogenesis of myocardial ischaemia during upper gastrointestinal endoscopy. Cardioprotective measures other than oxygen therapy should soon be evaluated before the implications of the new standards of care in endoscopy have become generally adopted.