In order to study the electrical changes that may occur during bronchoscopy in coronary patients we have carried out continuous electrocardiographic recordings during the course of endoscopy in 36 patients. We have been able to compare two groups: Group 1 consisting of 18 patients with coronary disease, and Group 2 with 18 non-coronary patients. There was no difference for sex, age or blood gases at the time of the examination in either group. Continuous electrocardiographic recording was started one hour before the examination and went on until two hours after, and was analysed as a function of the different durations of the endoscopy and any possible incidents. The blood potassium and the lidocaine blood levels at the end of the examination did not differ between the two groups. We observed no disorders of rhythm or of conduction. The only common change in the two groups was a frequent elevation of heart rate. There was no difference between the two groups. We have on the other hand been able to show in 3 coronary patients problems of repolarisation, which looked like current ischaemia occurring during the bronchoscopy and disappearing after the examination. We had no clinical upsets and do not have to regret having done any of the examinations, but these observations suggest we should be particularly careful in considering the indications for bronchoscopy, and the surveillance of patients during bronchoscopy where there is coronary disease.