ECG chest wall mapping with bicycle ergometry which can detect not only myocardial ischaemia but also individual coronary artery territories involved has been used to screen 100 consecutive patients presenting with claudication. Fifty-three had a positive history and/or evidence of ischaemic heart disease on a resting ECG. The test was positive in 38, negative in 38 and inconclusive in 24, the latter because of inadequate heart rate response. In 11 out of 38 (29%) with a positive test there was no history or evidence of myocardial ischaemia on a conventional resting ECG. ECG changes suggestive of three vessel coronary disease were found in three, single vessel coronary disease in 16 and two vessel disease in 19. Of the latter, eight had changes in the LAD/circumflex distribution, indicating left main stem or equivalent disease. These together with the three with triple vessel coronary disease constituted a subset of 11 (11%) high risk patients who merited coronary angiography with a view to confirming the presence of severe coronary disease.